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1. Response 1 testmode 2 TestID 3 data_HighByte 4 data_LowByte Dim Value As Single Dim i As Byte Dim Step As Integer Dim HighByte LowByte DTCode As String If Response 1 lt gt amp H42 Then Debug Print RESPONSE ERROR Else Select Case Response 2 Case amp H2 HighByte Hex Response 3 LowByte Hex Response 4 If Len HighByte 1 Then 0X stands for Powertrain DTCs HighByte PO amp HighByte DTCode HighByte amp LowByte datDTCs Recordset FindFirst DTC amp DTCode amp txtDTC 0 Text datDTCs Recordset Fields 0 Value txtRemarks 0 Text datDTCs Recordset Fields 1 Value Else Debug Print Other DTCs are not defined in SAE documents End If 96 Case amp H3 Fori 0 To 7 If Response 3 2 i Then txtCurrentData 0 Text FuelSystemStatus i Exit For End If Next 1 If Response 4 lt gt 0 Then Fori 0 To 7 If Response 4 7 2 i Then txtCurrentData 1 Text FuelSystemStatus i Exit For End If Next 1 End If Case amp H4 To amp HB amp HD Value Calculation CLng Response 3 Response 2 txtCurrentData Response 2 2 Text Value Case amp HC Dim DataInput As Long DataInput CLng Response 3 256 CLng Response 4 Value Calculation DataInput Response 2 txtCurrentData Response 2 2 Text Value End Select End If End Sub Private Function Calculation DataIn As Long Index As Byte As Single Dim Min 4 To amp H1B As Single Dim Scaling 4 To amp
2. ISO The International Organization for Standardization is a worldwide federation of national standard bodies who work for preparing International Standards 12 The ISO 9141 2 describes the physical and data link layer of a vehicle serial diagnostic bus The specifications of the protocol are 1 The maximum sink current be supported by the OBD II Scan Tool is 100mA 2 The range for all tests preformed relative to ISO 7637is 1 0 to 40 0V 3 The minimum bus idle period before the tool transmits an address shall be 300ms 27 The ISO 9141 2 protocol specifies the requirements for setting up communication between the on board emission related Electronic Control Units ECUs of the road vehicles and the SAE OBD II scan tool as specified in SAE J 1978 22 The vehicle ECUs in case of ISO 9141 2 protocol are required by OBD II to communicate with the SAE J1978 OBD II scan tool 22 must support either a one line K line only or a two wire K and L line communication connection to the SAE J 1978 OBD II scan tool through the SAE J1962 diagnostic connector 25 Line K is a bidirectional line It is used during initialization to convey address from diagnostic tester to vehicle ECUs simultaneously with the line L After conveying the address the K line is used to convey bi directional data The line L is unidirectional line and is only used during initialization simultaneously with the K line 13 Figure 3 1 shows the system configuration
3. 100 255 Scaling 5 1 Scaling 6 100 128 Scaling 7 100 128 Scaling 8 100 128 Scaling 9 100 128 Scaling 8 HA 3 Scaling amp HB 1 Scaling amp HC 1 4 Scaling amp HD 1 Scaling amp HE 1 2 Scaling amp HF 1 Scaling amp H10 0 01 Scaling amp H11 100 255 Scaling amp H14 0 005 Scaling amp H15 0 005 Scaling amp H16 0 005 Scaling amp H17 0 005 Scaling amp H18 0 005 Scaling amp H19 0 005 Scaling amp H1A 0 005 Scaling amp H1B 0 005 MAX ARRAY Calculation Min Index Scaling Index Dataln End Function Private Sub Form_load Dim I As Integer set all disabled and invisible first For I 2 To 30 Label2 I Enabled False 91 txtCurrentData T Visible False Next I then recover those selected PID For 1 0 To 99 If PID I 0 Then Exit For Elself PID I lt gt 19 Then PID 19 shows nothing Label2 PID I Enabled True txtCurrentData PID I Visible True End If Next I If PID 0 3 Then PID 3 show the 2 fuel system status Label2 2 Enabled True txtCurrentData 2 Visible True End If End Sub 92 This code is to display the Diagnostic trouble codes received from the automobile Private Sub Timer1_Timer Static pointer As Integer pointer pointer 1 Const maxium 30 If pointer gt maxium Then pointer 1 End If Response 1 amp H41 Response 2 pointer 3 Response 3 amp H1 Response 4 amp
4. CLng Response 4 Value Calculation Datalnput Response 2 txtCurrentData Response 2 Text Value Case amp H12 For I 0 To 7 If Response 3 2 I Then txtCurrentData amp H12 Text AirStatus I Exit For End If 89 Next I Case amp H13 Value Response 3 Step 256 For I 0 To 7 Step Step 2 If Value gt Step Then txtCurrentData amp H1B I Visible True Label2 amp H1B I Enabled True Value Value Step Else txtCurrentData amp H1B I Visible False Label2 amp H1B I Enabled False End If Next I Case amp H14 To amp HIB Value Calculation CLng Response 3 Response 2 txtCurrentData Response 2 Text Value Case amp HIE If Response 3 lt 1 Then txtCurrentData Response 2 Text AUX Response 3 Else txtCurrentData Response 2 Text SAE NOT DEFINED End If End Select End If End Sub Private Function Calculation DataIn As Long Index As Byte As Single Dim Min 4 To amp H1B As Single Dim Scaling 4 To amp H1B As Single Dim Max 4 To amp H1B As Single MIN ARRAY Min 4 07 Min 5 40 Min 6 100 Min 7 100 Min 8 100 Min 9 100 Min amp HA 0 Min amp HB 0 Min amp HC 0 Min amp HD 0 Min amp HE 64 Min amp HF 40 90 Min amp H10 0 Min amp H11 0 Min amp H14 0 Min amp H15 0 Min amp H16 0 Min amp H17 0 Min amp H18 0 Min amp H19 0 Min amp H1A 0 Min amp H1B 0 SCALING ARRAY Scaling 4
5. Private Sub cmdNext_Click End Sub Private Sub cmdOK Click Dim i J Total As Integer clear PID2 group For i 0 To 99 PID2 i 0 Next 1 get which has been checked For i amp H3 To amp HD If Check1 i 3 Value Checked Then PID2 Total 1 Total Total 1 End If Next 1 Debug Print Total Total For J 0 To Total 1 Debug Print PID2 Hex PID2 J Next J Provide some response here Response 1 H42 Response 2 amp H3 Response 3 amp H1 Response 4 amp H2 Unload Me frmDisplayFreezeData Show vbModeless End Sub 107 Private Sub Form_Load End Sub This code is to check the test status Private Sub Form_Load Dim reply As Byte Dim i As Integer construct request Request 1 amp H1 Request 2 amp H1 Fori 3 To7 Request i amp HO Next 1 Send Request reply SendRequest Request 1 Response 1 Response 1 amp H41 Response 2 amp H1 Response 3 amp HD Response 4 amp H77 Response 5 amp H77 Response 6 amp H77 Response 7 0 If Response 1 lt gt amp H41 Then Debug Print RESPONSE ERROR ElseIf Response 2 lt gt amp H1 Then Debug Print RESPONSE ERROR Else Get the of DTC and MIL Status If Response 3 gt 128 Then DTCNum Response 3 128 MIL True Else DTCNum Response 3 MIL False End If Get the status of Test Call BytetoBit Response 4 For1 0 To 2 Label2 1 Enabled Bit i
6. H bit 0 if ifr bit 0x08 for 1 0 1 lt 6 1 The frame does not have IFR res i frame 1 3 data 1 send only the data bytes to Application layer Check for number of data bytes if data lt 7 79 for i data 1 1 lt 7 14 res 1 0X00 padding with zeros j return res 1 returns the data to Application layer else for 1 0 1 lt 6 1 with IFR res 1 frame i 3 return res i returns the data to Application layer j j j j else for 1 0 1 lt 6 1 res 1 0X00 return res i returns error message to Application layer 80 PARC CCCI IC k k k k k k 4 k 1 k k k k k k k This program is written to send the request message from the Application layer to the Physical layer when user requests for a specific information EEEE o o k k k k k k k k k k k k ak 2k k k k k k k k k k k k k k 2k 2k ak k k ok 2 k k A include lt stdio h gt define crc void Physical unsigned char void main static int pronumber unsigned char dataframe 12 req 7 crc byte test mode int i data byte for 1 0 1 lt 6 1 reqii i j test mode req 0 when the request message is for the powertrain diagnostic data if test mode 0X01 data_byte 2 for 1 2 1 lt 6 1 req 1 0X00 j j else when the requested message is powertrain freeze frame data if test mode 0X02 81 data b
7. have considered in selecting the correct front volume include the configuration of the catalyst system washcoat formulation engine out emission level and others According to manufacturers a higher amount of variability exists with the catalyst monitor than with other OBD II monitors due to catalyst manufacturing processes vehicle production tolerances fuel quality and variability in real world driving patterns The malfunction criterion must be selected such that all vehicles will identify a catalyst malfunction before the tailpipe emission level exceeds 1 5 times the standard Manufacturers have stated that the wide distribution of monitoring system results caused by this variability may result in a malfunction indication at tailpipe emission levels below the standards on a percentage of vehicles Manufacturers have requested the ARB to accept catalyst monitoring strategies that operate over the Unified Cycle instead of over the Federal Test Procedure FTP cycle that the current regulation requires The Unified Cycle was developed by the ARB for emission inventory purposes and contains more high speed and load driving conditions than the FTP cycle The expanded speed and load regions on unified cycle would better facilitate reliable monitoring due to the higher exhaust flow rates and catalyst temperatures Increasing the malfunction criterion to 1 75 times the HC standard should allow manufacturers to on average indicate a catalyst mal
8. single byte and consolidated the data field can usually be encoded in the same way There are different ways in which information can be formatted in the data field The data field immediately follows the header field The number of bytes in this field will vary based upon the content of the header field The maximum data field length is limited by the requirements of SAE J1850 Because of differences in functionally and physically addressed messages or within frame response data these cases are defined separately 4 6 1 Functional Data Field Formats There are five different formats for functional data fields depending on the number of data bytes and secondary address 4 6 1 1 Functional Data Field Format 0 amp 1 There are no additional bytes of data in case of data field with 0 format It only has header CRC and IFR bytes In case of Format 1 it includes data only parametric data Used for message types 0 and1 39 4 6 1 2 Functional Data Field Format 2 In this format the data field contains a secondary address byte which is used to determine the target function being addressed said i ll EN lk Re Secondary ID 6 bytes Functional Data Field see er T Ten Figure 4 7 Secondary Address Byte Format l Q is the quality bit and C is the control bit used to distinguish between request report and query message operations The combinations of primary and secondary addresse
9. 1 Const maxium 9 If pointer gt maxium Then pointer 1 102 End If Response 1 amp H45 Response 2 pointer Response 3 amp H10 Response 4 amp H33 Call Form_ Activate For the true call to OBDII Static i As Integer 1 i 1 If 1 gt TestIDSelNum Then 1 0 reset TestID counter if bigger than selected TestID Num End If Request 1 amp H5 Request 2 TestID i For J 3 To7 Request J 0 Next J Dim reply As Byte reply SendRequest Request 1 Response 1 Call Form_Activate End Sub Code to control the request Private Sub cmdCancel_Click Unload Me End Sub Private Sub cmdOK Click Dim 1 As Integer Dim reply As Byte If Check1 0 Value Checked Then send request Response 1 amp H8 Response 2 amp H1 For1 3 To7 Response 1 amp HO0 Next 1 reply SendRequest Request 1 Response 1 MsgBox Control request has been sent 103 Unload Me Else MsgBox Please select the Control Test Exit Sub End If Reply SendRequest Mode PID Details continued End Sub Private Sub Form_Load End Sub 104 This code is to request DTC by status Private Sub cmdCancel_Click Unload Me End Sub Private Sub cmdOK_Click Dim i As Integer Dim Status As Integer Status 0 Fori 0 To 7 If Check1 i Value Checked Then Status Status 2 7 i End If Next 1 If Status 0 Then MsgBox Please check at least one status End If End Sub P
10. 108 If Bit i False Then Check1 i Value Gray End If Next 1 Fori 4 To 6 If Bit i Then Check1 i 4 Value Checked End If Next 1 Call BytetoBit Response 5 Fori 0 To 7 Label2 3 i Enabled Bit i Next i Call BytetoBit Response 6 Fori 0 To 7 If Bit i Then Check1 3 i Value Checked End If Next 1 End If End Sub To select the oxygen sensor ID code For J 0 To TestIDSelNum 1 Debug Print TestID Hex TestID J Next J get which sensor has been selected if not notice user SensorSelected False For J 0To 7 If Option1 J Value True Then SensorLoc J SensorSelected True Exit For End If Next J If SensorSelected False Then MsgBox Please Select Sensor Location Exit Sub End If Debug Print SensorLoc SensorLoc 109 Unload Me frmDisplayO2Sensor Show vbModeless End Sub Private Sub Label2_Click Index As Integer End Sub 110 PERMISSION TO COPY In presenting this thesis in partial fulfillment of the requirements for a master s degree at Texas Tech University or Texas Tech University Health Sciences Center I agree that the Library and my major department shall make it freely available for research purposes Permission to copy this thesis for scholarly purposes may be granted by the Director of the Library or my major professor It is understood that any copying or publication of this thesis for financial gain shall not be allowed without my further written permiss
11. 72178 Header Field Data Field CRC byte SCOPE OF SAE J2178 FOR A SAE J1850 FRAME WITHOUT INFRAME RESPONSE IFR SAE J2178 SAE J21 SCOPE OF SAE J2178 FOR A SAE 71850 FRAME WITH INFRAME RESPONSE 78 Header Field Figure 4 1 SAE 71850 Frame Structure with and without IFR In Frame Response 4 5 Header Field SAE 71850 supports only two formats of message headers They are single byte header and the consolidated header format The consolidated header format has two forms a single byte form and a three byte form These two forms of consolidate header are identified by the value of H bit The information in the header field for both formats contains target source priority and message type information and or diagnostic test modes There are two types of messages one is the request that is the command or queries for data The second one is the response that is reports or acknowledgment 34 Depending on the type of message the information in the header byte changes Figure 4 2 glves an overview of the header field SAE J1850 Single Byte Header Consolidated Header 76543210 y One Byte Three Byte form form Data field Physical format Address Figure 4 2 Overview of SAE J1850 Header Field Single Byte header 4 5 1 Single Byte Header Message Format For a single byte header the entire byte is used to define the message identifier ID as
12. California Code of Regulations COR ooo coccion 10 23 Environment Protection Agency EPA 000 0 0 eer 11 2 9 Clana A A 12 2 4 On board diagnostics test standards sss sss 13 2 4 1 On board diagnostics test proCedures oooocooocooccccccconcccccccooss 15 2 4 2 On board diagnostics test report loses esee 17 2 4 3 On board diagnostics test equipment requirements 18 2 5 Technical Status and Proposed Monitoring System Amendments IV 19 2 5 Catalyst Monto oe islas ads 19 2 52 Misfire RIODIOLITIE int ld piste to Cu ub E iii 2 5 3 Evaporative System Monitoring 0 0 00 000 emm 22 2 5 4 Positive Crankcase Ventilation PCV System Monitoring 29 3 PROTOCOLINTBEREACGE etit teet sept bolla vio 25 PANU OUUCHON A stata Sanauenseide 25 3 2 Class B Data Communication Network Interface J1850 25 3 2 1 Network Architecture Support 0 0 0 0 0 0 0 0 cee ece tenet eee ees 26 3 22 Data Bus Popology xa iui T e o 26 0 22 35 Data Bus Control iu cte etis A 27 3 3 ISO 9141 2 1994 E Road Vehicles Diagnostic Systems CRAB 27 39 T Application Laye esm ha EAE PE GEN bt iet 29 3 3 2 Data Link Payer die teo d pote o etes mis 29 393 PHY SICAMLAVER iin srr tahoe ia tuscan tae tes p 30 A DATA LINKE LAYER eue eet Cete ttes 32 Ss oaa Ss So esee A i a aes cute 32 de DP AGUPESSING Strategy d ood etre dicta ads 32 4 3 Network E
13. H33 Call Form_ Activate For the true call to OBDII Static I As Integer I I 1 If I gt PIDSelNum Then I 0 reset PID2 counter if bigger than selected TestID Num End If Request 1 amp H2 Request 2 PID I For J 3 To7 Request J 0 Next J Dim reply As Byte reply SendRequest Request 1 Response 1 Call Form_Activate End Sub Private Sub Form_Activate Dim reply As Byte Dim i As Integer Dim temp temp2 As String Request 1 amp H3 Fori 2To7 Request 1 amp HO Next 1 93 reply SendRequest Request 1 Response 1 DTCNum 2 Debug Print Hex Response 1 If Response 1 lt gt amp H43 Then MsgBox Response Message Error Exit Sub Elself Response 2 lt amp H10 Then temp 1 Hex Response 2 temp2 Hex Response 3 If Len temp1 lt 2 Then temp 0 amp temp If Len temp2 lt 2 Then temp2 0 amp temp2 DTCString 0 P amp templ amp temp2 Debug Print DTCI DTCString 0 If Response 4 lt gt amp HO0 Then templ Hex Response 4 temp2 Hex Response 5 If Len temp1 lt 2 Then temp1 0 amp templ If Len temp2 lt 2 Then temp2 0 amp temp2 DTCString 1 P amp temp amp temp2 Debug Print DTC2 DTCString 1 End If If Response 6 lt gt amp HO Then temp1 Hex Response 6 temp2 Hex Response 7 If Len temp1 lt 2 Then temp1 0 amp temp1 If Len temp2 lt 2 Then temp2 0 amp temp2 DTCString 2 P amp templ amp temp2
14. Recommended practice for Diagnostic Trouble Code Definitions SAE J2012 JUL96 Diagnostics for Light and Medium Duty Vehicles Standard Manual Warrendale PA 1997 pp 39 45 22 Society of Automotive Engineers Inc OBD II scan tool SAE J1978 JUN94 Diagnostics for Light and Medium Duty Vehicles Standard Manual Warrendale PA 1997 pp 25 28 23 Society of Automotive Engineers Inc Enhanced E E Diagnostic Test Modes SAE J2190 JUN 93 Diagnostics for Light and Medium Duty Vehicles Standard Manual Warrendale PA 1997 pp 48 64 24 Geng Fu Application Layer Texas Tech University Unpublished report 75 25 Society of Automotive Engineers Inc diagnostic connector SAE J1962 JAN 95 Diagnostics for Light and Medium Duty Vehicles Standard Manual Warrendale PA 1997 pp 19 24 26 Vetronix Mastertech Vetronix Corp Diagnostics for Vehicle Electronics Santa Barbara California 1997 76 APPENDIX SOURCE CODE FOR THE APPLICATION LAYER AND DATA LINK LAYER This appendix contains the listing of the source code developed for implementation of data link layer and application in the design of Universal scan tool Source code for data link layer is in C and for Application layer source code is in Visual Basic Ak kkkkkk k kk k kk kkkk k k kkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkk k k kkkkkk xk This program written to implement data link layer in the Universal scan tool
15. This program includes four different modules All four modules are included PEPR A od k k k ole le kk k de ade ade ok ok ok ok ok ll le le ok k oke oe k e ke a oe K ke a ll le ff je K K K K 2K K K K K K K K K This program is written to transfer the response received from the Physical layer to the Application layer include lt stdio h gt include lt stdlib h gt define crc unsigned char phy_app unsigned char Physical int size main unsigned char head byte Physical 12 temp ifr bit res 7 crc byte frame 11 unsigned char old crc old int size data 1 input data is obtained from the Physical layer 77 for 1 0 1 lt 11 14 Physical 1 1 1 size i if size lt 12 crc byte Physical size The last byte of the frame is the crc which is compared for 1 0 1 size i with that of the calculated crc frame i Physical i j old new crc dataframe old crc old if crc byte old crc temp frame 0 head_byte temp amp 0x10 if head_byte 0x10 single byte header ifr_bit temp amp 0x08 if ifr_bit 0x08 check for IFR for 1 0 1 lt 6 1 TER not allowed res i frame it1 data 1 78 if data lt 7 for i data 1 1 lt 7 14 res 1 0X00 return res i else for 1 0 1 lt 6 1 res i frame i 1 return res i returns the data to Application layer else ifr bit temp amp 0x08 Three byte header
16. case of an error the response is sent back to the Physical layer and the Application layer is informed All other bytes of the response are masked and only data bytes are transferred to the Application layer Because of the constraints with the standard display format the Application layer can only interpret seven bytes of data In order to avoid any misinterpretation of data by the Application layer additional zeros are padded to the data if the number of bytes is less than seven 55 DO A o ii A A PHYSICAL LAYER Data from Physical layer CRC Check yes d No of Header Bytes Single Byte Header Three Byte Header Mask only header btye s yes Mask Header and IFR Byte s Pad with zeros to fill Tbytes Data bytes TO APPLICATION LAYER Figure 6 1 Data Transfer from the Physical to the Application Layer 56 6 4 Request Message The request message is the command placed by the Application layer to obtain particular information from the vehicle When the user requests some information by pressing a key on the scan tool seven bytes of data are sent to the data link laver The protocol being supported by the vehicle is determined during the initialization and is stored for the rest of the transactions Depending on the protocol being supported by the vehicle and the test mode of the message the header byte is constructed The CRC byte can be calculated from the algorithm des
17. implemented according to OBD II minimum requirements Refer SAE J2190 23 for additional information on enhanced test modes In addition to the functions described above the Application layer must include some additional provisions to ensure proper operation of both the test equipment and the vehicle during diagnostic procedures 5 5 Multiple Response to a Single Data Request In case of a functional message test equipment will request data without knowledge of which module on the vehicle will respond In some cases multiple modules may respond with the information requested In addition a single module may respond with multiple responses for a single request Any test equipment requesting information must have provision for receiving the multiple responses 5 6 Response Time The on board system should respond to a request within 100ms of a request or a previous response In case of multiple responses for a single request this allows as much time as is necessary for all modules to access the datalink and transmit their responses If there is no response within this time the tool can assume no response will be received 5 5 7 Minimum Time between Requests from Scan Tool A scan tool should always wait for a response from the previous request or no response timeout before sending another request In no case should a request be sent less than 100ms after the previous request 5 8 Data Not Available There are two co
18. indicating the role of each of the communication lines L and K Diagnostic tester in accordance Connector in accordance with SAE J 1962 The arrows indicate the direction of data flow Figure 3 1 ISO 9141 2 System Configuration 28 The OBD II emission related communications consist of messages of between 5 and 11 bytes The sequence and description of all the bytes except the error checking byte is the same as that in the SAE J 1850 protocol Each of these bytes is described in Chapter 4 Instead of CRC Cyclic Redundancy Check as in SAE J1850 protocol the checker sum is used The algorithm is described in detail in ISO 9141 2 protocol 13 The Class B network maps into the OSI ISO open System Interconnect model as described in the following paragraphs The mapping of SAE J1850 to the ISO model is shown in Figure 3 2 3 3 1 Application Layer At the top of the OSI reference model is the Application Layer This layer establishes the relationship between application input and output devices including what is expected of human operators This layer documents the high level description of the function including control algorithms if appropriate 3 3 2 Data Link Layer The primary function of the Data Link Layer is to convert bits and or symbols to validated error free frames or data Typical services provided are serialization parallel to serial conversion and clock recovery or bit synchronization An important additio
19. the DTC occurred Figure 7 3 shows the various parameters when one of the DTCs described above was stored 65 Figure 7 1 Scan Tool Data Link Interface 66 ia D iagnostic Trouble Codes Display Diagnostic Figure 7 2 Display of DTCs on the Scan Tool 67 a Freeze Frame Data Display Figure 7 3 Freeze Frame Data Display 68 7 3 PC Interface Interface of the scan tool with the PC is important as it aids in capturing the required data analyzing it and using it for future reference The data transfer should enable the transfer of both the stored data in the tester and the real time data when the engine is running to the PC The information can be stored at various intervals of time which enables the complete understanding of the behavior of the vehicle The program developed in this project can be called by another software program to display all the stored data in various modes like bar charts line graphs etc Figure 7 4 shows the data captured from the scan tool which when interpreted gives the condition of the vehicle at that instant Engine Speed 0 RPM ECT 59 C Vehicle Spd km h Ign Timing 2 0 Engine Load 0 0 96 MAP P 99 kPaA MAF H 0 0 gm s TPS 36 0 0 IAT 38 C Fuel Stat 1 OL Fuel Stat 2 OL STFT1 0 0 96 LT FT 1 0 0 96 ST FT 2 0 0 gt LT FT 2 0 0 025B151 0 195 YDC FT 025 B1 1 0 0 025B152 0 755 VDC 025B153 0 850 VDC O25 B251 0 75
20. will improve the efficiency and accuracy of OBD II test equipment In this project only the minimum requirements of the OBD Il test equipment have been achieved Since most of the manufacturers are implementing the ISO 9141 2 protocol it can also be implemented with very few changes Only the error checking byte in ISO 9141 2 protocol differs compared to SAE J1850 protocol In case of ISO 9141 2 checker sum algorithm is implemented instead of cyclic redundancy check as in SAE J1850 protocol The design in this project can be slightly modified to implement the ISO 9141 2 protocol This system can be upgraded as the standards are reviewed and new modifications are made 73 1 2 3 4 5 6 7 8 9 BIBLIOGRAPHY Proposed rule making Modification of Federal On Board Diagnostic Regulations Extension of Acceptance of California OBD II Requirements Environment Protection Agency 40 CER Part 86 EPA May 1997 Gerard Diagnostic Tools www rug nl rug homepage wink scantool htm FIA Freedom of choice www fia com homepage selection a html November 1996 SAE J1978 JUN 94 OBD II Scan Tool SAE On BoardDiagnostics and multiplex Technical Reports SAE international 1997 Staff Report Technical Status Update and Procedure Revisions to Malfunction and Diagnostic System Requirements Applicable to1994 and Subsequent California Passenger Cars Light Duty Trucks and Medium Duty Vehicl
21. 5 VDC FT 025 B2 1 0 0 MIL Status Off Stored DICs 0 OBD Cert OBDII Figure 7 4 The Data Captured from the Scan Tool The captured data can be stored can be displayed in various formats like line graphs and bar graphs for easy and quick interpretation of the vehicle condition and to 69 diagnose the actual problem Figure 7 5 shows the bar graph of the captured data and Figure 7 6 shows the line graph 09 C 0 ORPM 0 195VDC 215 6 6000 1 300 164 5 4800 1 040 113 4 3600 0 780 62 y 2 2400 0 520 11 1 1200 0 260 40 i 0 0 0007 ECT Stored DTCs Engine Speed 025 B1 1 7 5 Bar Graph of the Captured Data 70 o nanan E 1 TU MAUI edades s TU JR A m i U 195VDC 7 6 Line Graph of the Captured Data 71 CHAPTER 8 CONCLUSIONS The objective of this thesis was to develop a Universal scan tool which was required to interface with the on board diagnostics system for receiving and down loading emission related data and transmit this data to the TX96 equipment for communication with the Texas Data Link system The results in the previous chapter show that this project was successful in accomplishing most of the goals set at the beginning of the project The system implemented in this project supports all the basic requirements of the OBD II test equipment The Universal scan tool developed in this project can be used on any model vehicle and of any specific
22. 898 an updated version of the California OBD II requirements acceptable for federal OBD compliance This action also amended the federal OBD requirements to harmonize with 12 those of the California OBD II requirements for 1999 and later model year light duty vehicles LDVs and light duty trucks LDTs This will result in federal OBD malfunction thresholds consistent with the California OBD II thresholds and it will require monitoring of all emission related power train components similar to the California OBD II regulations The EPA believes that this harmonization is consistent with the requirements of section 202 m of the CAA and will not compromise the stringency of the federal OBD program 10 The on board diagnostic test standards test procedures test report and test equipment requirements are discussed here as in clean Air act 10 2 4 On board diagnostics test standards The on board diagnostics test standards are defined in the section 85 2205 85 2206 in the clean air act 10 I Beginning January 1 2000 failure of the on board diagnostic test shall be a basis for failure of the Inspection and Maintenance I amp M test Prior to this date it may be a basis for failure of the Inspection and Maintenance I amp M test but it is not mandatory 2 A vehicle may fail the on board diagnostics test if it is a 1996 or newer vehicle and the vehicle connector is missing has been tampered with or is otherwise inoperable 3 A vehi
23. 979 e Provide user manual or help facility The data link layer of the Universal scan tool designed in this project was implemented using C code and the Application layer of the Universal scan tool designed in this project was implemented using Visual Basic code The code is included in Appendix The next chapter will provide an insight into what OBDII is and its backeround Chapter 3 explains the protocols and communication network used Chapter 4 describes the data link layer Chapter 5 deals with the standard display format and the test modes Implementation of the Universal scan tool is described in Chapter 6 The final chapter provides results and conclusions and also suggests further improvements CHAPTER 2 ON BOARD DIAGNOSTIC SYSTEMS 2 1 Introduction The on board diagnostic system is like any diagnostic system used to detect malfunctions in the automobile The on board diagnostic system reduces the time between the occurrence of a malfunction and its detection and repair This will not only reduce emissions caused by a malfunction but will minimize consequential damage to other vehicle components or systems Virtually all current motor vehicle emission control systems are integrated into a broad microprocessor based power train management controller By incorporating additional software to analyze data already available to the controller and with the addition of only a few electronic hardware components for providi
24. Ate etr baie 77 ABSTRACT This project deals with developing a system which can be implemented by TNRCC Texas natural resource conservation Commission as a part of State implementation plan to verify compliance with EPA Environment Protection Agency program performance standards In the process a Universal scan tool has been designed in accordance with the EPA and Society of Automotive Engineers SAE specifications The system developed here not only acts as scan tool to diagnosis the trouble code but also aids in computer interface which helps TNCC to maintain a database of all the cars in Texas with their emission related data A design of universal scan tool is discussed from software perspective The results of this system were compared by actually plugging in a scan tool into the 1996 and 1997 model vehicles The conclusions and recommendations for future work are discussed vil LIST OF TABLES AN A A dico donc eee tes 14 2 2 Listing of OBD Codes when Retrieved sss 17 4 1 Description of Byte 1 of Three Byte Consolidate Header s 37 5 1 Message Data Bytes oc oe RS 47 6 1 Standard Diagnostic Message Format ssssssssssssss e 54 7 1 Message Data Bytes to Retrieve DTC sse ee 64 viii 3 3 2 4 4 2 4 3 44 4 5 4 6 4 7 5 6 6 2 6 3 6 4 6 5 6 6 7 7 2 7 3 7 4 LIST OF FIGU
25. DESIGN OF A UNIVERSAL SCAN TOOL by SUNITHA GODAVARTY B E A THESIS IN ELECTRICAL ENGINEERING Submitted to the Graduate Faculty of Texas Tech University in Partial Fulfillment of the Requirements for the Degree of MASTER OF SCIENCE IN ELECTRICAL ENGINEERING Approved 2 e 1 ze ee May 1998 ACKNOWLEDGEMENTS I wish to express my sincere gratitude to Dr Micheal Parten my graduate advisor for his guidance valuble suggestions encouragement and moral support thruoghout the period of my study and research at the Texas Tech University I am grateful to Dr Sunanda Mitra and Dr Mary Baker for serving as members of my thesis committee I would like to thank all the members of OBD Il scan tool design project for their enormous contributions to the project I would like to thank the Department of Electrical Engineering for providing financial assistance throught my graduate studies I am most grateful to my parents and my family for their support and encouragement Finally I would like to thank all my friends for their encouragement and support TABLE OF CONTENTS ACKNOWLEDGEMENTS ti A t s ii A e aa E A RU AER vii LISTOF TABLES a tea a ENN viil EISTOREFIGURES aaa dia adds Ix CHAPTER Iz INTRODUCTION S oves a oco ir crate dtd ote ce manera aes l in AAA a EEEE c ise odis 1 o A E 2 ES Statement of the proble ii 3 2 ON BOARD DIAGNOSTIC SYSTEMS 0 ccc cece el 8 2d AML OU CHONG roe arate lis 8 2 2
26. Debug Print DTC3 DTCString 2 End If Else MsgBox DTC is not defined in SAE Documents End If DTCGroup 0 Call DTCShowGroup DTCGroup End Sub Private Sub DTCShowGroup Base As Integer Const GroupNum 5 For i 0 To GroupNum 1 If DTCString i Base Then txtDTC i Text 94 txtRemarks 1 Text Else For how to convert the DTC into DTCString relate the Display Freeze Frame datDTCs Recordset FindFirst DTC amp DTCString i Base amp txtDTC i Text datDTCs Recordset Fields 0 Value txtRemarks i Text datDTCs Recordset Fields 1 Value End If Next i End Sub Private Sub Form_Load cmdBack Enabled False If DTCNum lt 5 Then cmdMore Enabled False End If End Sub 95 This code is to display the freeze frame data Private Sub cmdCancel_Click Unload Me End Sub Private Sub Form Activate Define the Fuel System Status Dim FuelSystemStatus 0 To 7 As String FuelSystemStatus 0 Open Loop has not yet satisfied condition to go closed loop FuelSystemStatus 1 Closed Loop using oxygen sensor s as feedback for fuel control FuelSystemStatus 2 Open Loop due to driving conditions power enrichment deceleration enleanment FuelSystemStatus 3 Closed Loop but fault with at least one oxygen sensor maybe using single oxygen sensor for fuel control FuelSystemStatus 4 FuelSystemStatus 5 FuelSystemStatus 6 FuelSystemStatus 7
27. H1B As Single Dim Max 4 To amp H1B As Single MIN ARRAY Min 4 0 Min 5 40 Min 6 100 Min 7 100 Min 8 100 Min 9 100 Min amp HA 0 Min amp HB 0 Min amp HC 0 Min amp HD 0 Min amp HE 64 Min amp HF 40 Min amp H10 0 Min amp H11 0 97 Min amp H14 0 Min amp H15 0 Min amp H16 0 Min amp H17 0 Min amp H18 0 Min amp H19 0 Min amp H1A 0 Min amp HIB 0 SCALING ARRAY Scaling 4 100 255 Scaling 5 1 Scaling 6 100 128 Scaling 7 100 128 Scaling 8 100 128 Scaling 9 100 128 Scaling amp HA 3 Scaling amp HB 1 Scaling amp HC 1 4 Scaling amp HD 1 Scaling amp HE 1 2 Scaling amp HF 1 Scaling amp H10 0 01 Scaling amp H11 100 255 Scaling amp H14 0 005 Scaling amp H15 0 005 Scaling amp H16 0 005 Scaling amp H17 0 005 Scaling amp H18 0 005 Scaling amp H19 0 005 Scaling amp H1 A 0 005 Scaling amp H1B 0 005 MAX ARRAY Calculation Min Index Scaling Index Dataln End Function Private Sub Form_Load Dim Mode PID As String Dim i As Integer Mode 02 PID 02 98 call SendRequest Mode PID simulate response Response 1 amp H42 Response 2 amp H2 Response 3 amp H1 P0134 Response 4 amp H34 set all disabled and invisible first Fori 0To 11 Label2 i Enabled False txtCurrentData i Visible False Next 1 then recove
28. OID IpReserved unsigned char PASCAL SendRequest unsigned char x unsigned char y unsigned char Req 7 Res 7 int 1 get the request from the passed parameters for 1 0 1 lt 7 i Req i x sizeof unsigned char 1 get response from the somewhere for 1 0 1 lt 7 i Res i Req 1 1 j return the repsonse to Application layer for 1 0 i lt 7 i y sizeof unsigned char i Res 1 return x y 87 RRR RR KK RRR KR RRR e dee eoe de deeds KR RARA RARA eek ek oec Ko e c ee XE XX J APPLICATION LAYER In this part of the appendix visual basic code is included to implement the ty Application layer Various form files are included to display and request the current data freeze frame data diagnostic trouble codes oxygen sensor data El request control and help topics ui RRC o a o COCO k k k k k k kk k kk k k k k k k k k k k 2 4 k This code is to display the current data received from the automobile Private Sub cmdCancel_Click Unload Me End Sub Private Sub cmdRefresh Click Call Timerl Timer End Sub Private Sub Form_Activate Define the Fuel System Status Dim FuelSystemStatus 0 To 7 As String FuelSystemStatus 0 Open Loop has not yet satisfied condition to go closed loop FuelSystemStatus 1 Closed Loop using oxygen sensor s as feedback for fuel control FuelSystemStatus 2 Open Loop due to driving conditions
29. RES Basic Block Diagram of Scan TOOL ooo e 5 ISO 9141 2 System Configuration eee 28 Map of SAE J1850 to the ISO Model coo eme 31 SAE J1850 Frame Structure with and without IFR In Frame Response 34 Overview of SAE J1850 Header Field ccoo ocio ono 35 Single Byte Header Format sis 35 One Byte Form of Consolidate Header aa 36 Three Byte Form of Consolidate Header sese 37 Karger Address ras dpi 38 Secondary Address Byte Format sss seen 40 Diaenos e Trouble C OUS ooh A edo dida de ds cant 48 Data Transfer from Physical Layer to the Application Layer 56 Data Transfer from Application Layer to Physical Layer 58 Flowchart of Application Layer sssssssssssse e 60 Description of the Readiness Tetu Ie ree E E ita 61 Display of Diagnostic Trouble Codes eese eene 62 Display ob Current Dala POMAR 63 Scan Tool Data Link tera ani eee red tod oni eto Reda 66 Display of DTCs on the Scan TOOL coco cocco coccion ccoo essel 67 Freeze Frame Data Display sess e eee aes 68 The Data Captured trom the Scan TOO sud ice ot inane Ginette Lass Act 69 7 5 Bar Graph of the Captured Data 7 6 Line Graph of the Captured Data EET E E 9 See ise BOT eo rms pe NR N Gee E ave diese y eem AGNES AR er CRUS e CHAPTER 1 INTRODUCTION 1 1 Introduction As the quality of air is decreasin
30. applications Two specific implementations of this network are described based on the Physical layer differences One Physical layer is optimized for a data rate of 10 4Kbps while the other Physical layer is optimized for a data rate of 43 6Kbps Depending on the specific application and corporate philosophy towards network usage a manufacturer can implement either of the protocols 25 3 2 1 Network Architecture Support It is the intent of this network to interconnect different electric modules on the vehicle using an Open Architecture approach An open architecture network is one in which the addition or deletion of one or more modules data nodes has minimal hardware and or software impact on the remaining modules In order to support an open architecture approach the Class B network utilizes the concept of Carrier Sense Multiple Access CSMA with nondestructive contention resolution Additionally this network supports the prioritization of frames such that in the case of contention the higher priority frames will always win arbitration and be completed 11 3 2 2 Data Bus Topology Data bus topology is the map of physical connections of the data bus nodes to the data bus It includes all nodes and data buses involved in the data bus integration of the vehicle A single level bus topology the simplest topology is currently being used in several automotive applications The redundancy requirements of a particular application
31. cle may fail the on board diagnostics test if the malfunction indicator light is commanded to be illuminated according to visual inspection 4 A vehicle may fail the on board diagnostics test if the malfunction indicator light is commanded to be illuminated and any of the following OBD codes are present The codes are given in Table 2 1 13 ODE PXI ANY PX2XX ANY PX3XX ANY PXAXX E s 5 7 10 m o P0550 P055 P0552 P0553 P0554 P0560 P0561 P0562 P0563 R Cn N N N N Wl N o0 ON AR N a wp wg WI TS O OF OF CO CO O Oj O Aaj Aaf dj dal af ca amp A tA O O ol o Of ojl O E O A A HT 9 t O X gt NO N P0703 P0705 P0706 P0707 P0708 P0709 P0719 CA N N 00 9 m EN Table 2 1 OBD Codes COMPONENT E Fuel and Air Metering codes Fuel and Air Metering codes Ignition System or Misfire codes Auxiliary Emission control codes Vehicle Speed Sensor Malfunction Vehicle Speed Sensor Range Malfunction Vehicle Speed Sensor Circuit Low Input Vehicle Speed Sensor Intermittent erratic High Idle Control System Malfunction Idle Control System RPM Lower Then Expected Idle Control System RPM Higher Then Expected Closed Throttle Position Switch Malfunction Power Steering Pressure Sensor Circuit Malfunction Power Steering Pressure Sensor Circuit Malfunction Power Steering Pressure Sensor Circuit Low Inp
32. codes When the input to the data link layer is as shown below the respective DTCs corresponding to the Code 1 Code 2 and Code 3 are displayed on the scan tool Table 7 1 Message Data Bytes to Retrieve DTC Data Bytes O MN IR T T amp AAA Request current diagnostic data Hu e SPP LL LEE e NNNM Report Current Power train Diagnostic Data eT vr semi ode Ge ww oo For example if a response obtained from the Physical layer is given by 64 Alora which can be interpreted as module C3 of the vehicle has two stored DTCs Figure 7 1 shows the actual display what the user can see on interfacing the scan tool with the automobile The display shows both the request to the data link layer from the Application layer when a specific key is pressed and the response from the data link layer When the DTC display is selected the DTC and the description of the particular diagnostic trouble code is displayed which shown in the Figure 7 2 The first DTC is P0143 for Oxygen Sensor Low Voltage and the second is P0205 for injector function malfunction Cylinder 5 21 Figure 7 2 shows that the same result is displayed by the system 7 2 Freeze Frame Data Display The emission related data values which were stored during the freeze frame required by OBD regulations can be retrieved 20 The retrieved data helps the service technician to examine minutely the condition of the vehicle when
33. codes is as shown in Figure 5 1 Figure 5 1 Diagnostic Trouble Code 48 The purpose of this mode is to provide a means for the external test device to command on mode modules to clear all emission related diagnostic information This includes 1 Clear number of diagnostic trouble codes Mode 01 PID 01 2 Clear diagnostic trouble codes Mode 03 3 Clear trouble code for Freeze frame data Mode 01 PID 02 4 Clear Freeze frame data Mode 02 5 Clear oxygen sensor test data 6 Reset status of system monitoring tests Mode 01 PID 01 7 Clear on board monitoring test results Mode 06 PID 07 All modules must respond to this test mode request with ignition ON and with engine not running S 4 5 Mode 05 Request Oxygen Sensor Monitoring Test results The purpose of this mode is to allow the access to the on board sensor monitoring test results as required in OBD II regulations The use of this mode is optional depending on the method used by the vehicle manufacturers to comply with the requirements for oxygen sensor The result of the test results includes a test ID value that indicates the information requested 49 5 4 6 Mode 06 Request On Board Monitoring Test results for non continuously monitored System The purpose of this test mode is to allow access to the results for on board diagnostic monitoring tests of specific components systems that are not continuously monitored for example catalys
34. cribed in Chapter 4 This whole frame is transferred to the Physical layer The Physical layer sends the request message to the automobile Figure 6 2 gives an over view of the data transfer between the Application layer and the Physical layer 57 USER Scan Tool Key Pressed Data Bytes from application layer Determine the protocol supported Construct message Header Frame To Physical Layer Figure 6 2 Data Transfer from Application Layer to Physical Layer 58 6 5 Standard Display One of the aims of this project is to design a Universal scan tool which is efficient and easy to use The primitive scan tools could not describe the diagnostic trouble code they could only display the DTC and consequently ordinary people could not figure out the problem without verifying the thick manual To avoid these inconveniences this system display the actual code followed by the description of the DTCs All the requirements described in Chapter 5 have been met The system implemented in this project furnishes a user friendly display format It also includes a help facility which includes all the SAE J1979 20 definitions how to select the functions and also how to determine the PID ID item name and module id of data returned for display The scan tool display was built with the help of Visual Basic software 24 Figure 6 3 describes the Application layer flowchart Figures 6 4 give the description of the readiness test Figure
35. e to repair a wide range of relatively simple faults 3 1 3 Statement of the problem Under the safety inspection program operated by the Texas Department of Public Safety all vehicles are tested annually at a test and repair or test only facility using TNRCC certified test equipment TX96 The Texas Motorist s Choice Emissions 3 Testing Program which is part of the annual safety inspection program in the three geographical areas of Texas core program counties Harris Dallas Tarrant and El Paso includes OBD II testing The diagnostic requirements based on Title 13 California Code of Regulations section 1968 1 6 are designated as OBD II with a goal of monitoring all of the emission related components on board the vehicle for proper operation To implement the OBD II testing a OBD II test equipment was required to interface with the on board diagnostics system for receiving and downloading emission related data and transmit this data to the TX96 equipment for communication with the Texas Data Link system This project deals with the design of an OBD II test equipment which is Universal and that can be used to test any car that supports the On Board Diagnosticss I protocol This project was funded in part by the Mobile Source Division of the TNRCC Texas Natural Resource Conservation commission An attempt has been made to design a Universal scan tool which can diagnosis any problem with any vehicle equipped with an on board d
36. equirements The basic requirements of the scan tool or the OBD II test equipment are 1 The test system interface to the vehicle shall include a plug that confirms to SAE J1962 Diagnostic connector 2 The test system shall be capable of communicating via the J1962 connector with a vehicle certified as complying with on board diagnostic requirements 3 The test system shall be capable of checking for the monitors supported by the on board diagnostic system and the evaluation status of supported monitors in Mode 01 PID 01 as well as be able to request the diagnostic trouble codes as specified in SAE J 1997 In addition the system shall have the capability to include bi directional communication for control of the evaporative canister vent solenoid 4 The test system shall automatically make a pass fail or reject decision 2 5 Technical Status and Proposed Monitoring System Amendments IV 2 5 1 Catalyst Monitoring Emission control systems on virtually all new California vehicles include three way catalysts These catalysts consist of ceramic or metal honeycomb structures coated with precious metals such as platinum palladium or rhodium Three way catalysts are so designated because they are capable of simultaneously oxidizing HC and carbon monoxide CO emissions into water and carbon dioxide CO2 and of reducing oxides of nitrogen NOx emissions by reacting with CO and hydrogen into elemental nitrogen CO and water Oxy
37. er mile g mi hydrocarbons HC While the percentage of PCV failures causing high emissions appears to be small one percent of the vehicles tested the total emissions from tampered and improperly serviced PCV systems would raise the 2003 fleet average standard of 0 062 g mi HC by 0 012 g mi or nearly 20 percent So the proposed amendment would only require the detection of a disconnection in the system between both the crankcase and the PCV valve or between the PCV valve and the intake manifold Because disconnections between the valve and the intake manifold will result in a significant intake air leak effective monitoring should be readily achievable through the existing monitoring strategies for the idle air control system or the fuel system 24 CHAPTER 3 PROTOCOL INTERFACE 3 1 Introduction There are three types of communication interfaces to access the OBD II functions in a given vehicle They are SAE J1850 41 6 Kbps PWM SAE j1850 10 4 Kbps VPW and ISO 9141 2 of which only one can be used in any one vehicle to access all supported OBD II functions 3 2 Class B Data Communication Network Interface J1850 The SAE standard establishes the requirements for a Class B Data Communication Network Interface applicable to all on and off road land based vehicles It defines the minimum set of data communication requirements such that the resulting network is cost effective for simple applications and flexible enough to use in complex
38. es OBD ID California Air Resources Board August 1991 pp1 8 Staff Report and Notice of Public Hearing Title13 California Code of Regulations section 1968 www arb ca gov msprog obdprog obdprog htm December 1996 EPA EPA s Mission www epa gov epahome epa html USEPA EPA Air Quality www epa gov 25year air air html USEPA Air Resources Board Amendments to Regulations Regarding On Board Diagnostic System Requirements for 1994 and Later Passenger Cars Light Duty Trucks and Medium Duty Vehicles and Engines OBD II CARB July1997 10 Subpart W Emission control System Performance Warranty Short Tests Clean Air Act as amended 42 U S C 7541 b and 7601 a 11 Society of Automotive Engineers Inc Class B data Communications Network Interface SAE J1850 July 95 SAE Diagnostics for Light and Medium Duty Vehicles Standard Manual Warrendale PA 1997 pp 91 108 12 Draft International Standard ISO DIS 14230 2 Road Vehicles Diagnostic Systems Keyword protocol 2000 International Organization for Standards Geneva Switzerland June1995 13 International Standards Road Vehicles Diagnostic Systems CARB requirements for interchange of digital information International Organization for Standards Geneva Switzerland First edition 1994 02 01 74 14 Mohamed Sohel Sarwar Physical Layer Master s Thesis Texas Tech University unpublished 15 Soci
39. ess evaluation for applicable monitors accordance with SAE J1979 Beginning January 1 2000 if the readiness evaluation indicates that any on board tests are not complete the customer shall be instructed to return after the vehicle has been run under conditions that allows completion of all applicable on board tests If the readiness evaluation again indicates that any on board test is not complete the vehicle shall be failed 4 The test system shall evaluate the malfunction indicator light status bit and record status information in the vehicle test record a Ifthe malfunction indicator status bit indicates that the malfunction indicator light has been commanded to be illuminated the test shall send a Mode 03 request to determine the stored emission related power train trouble codes The system shall repeat this cycle until the number of codes reported equals the number of expected based on the Mode 1 response If any of the codes given above are present they shall be recorded in the vehicle test record and the vehicle shall fail the on board diagnostic inspection b If the malfunction indicator light bit is not commanded to be illuminated the vehicle shall pass the on board diagnostic inspection even if the OBD codes are present c If the malfunction indicator light bit is commanded to be illuminated the inspector shall visually inspect the malfunction indicator light to determine if it is 16 illuminated If the malfuncti
40. etwork They are physical addressing and functional addressing In the case of physical addressing frames are exchanged only between two devices based on their Physical address within the network Each node has a unique address within the network This type of addressing strategy is used when the communications involve specific nodes and not the others that may be on the network In the case of functional addressing frames are transmitted between many devices based on the function of the frame A node is assigned with a set of functions and can be located anywhere in the network Here the function of the message is important not the 32 physical address of the node The functional addressing is intended for messages that may be of interest to more than a single node 4 3 Network Element and Structure The general format of a message is Idle SOF DATA 0 DATA_N CRC EOD NB IFR_1 IFR N EOF IFS Idle The preceding acronyms are defined as follows Idle Idle Bus Occurs before SOF and after IFS SOF Start of Frame DATA Data byte each 8 bits long EOD end of data only when IFR is used CRC CRC error Detection Byte NB Normalization Bit 10 4Kbps only IFR In Frame Response Byte EOF End of frame IFS Inter Frame Separation 4 4 Class B Data Communication Network Message The general structure of SAE J 1850 message within frame response and without in frame is shown in Figure 4 1 33 SAE
41. ety of Automotive Engineers Inc Class B data communications Network messages part 3 Frame Ids for single byte forms of headers SAE J2178 3 SEP 93 SAE Diagnostics for Light and Medium Duty Vehicles Standard Manual Warrendale PA 1997 pp 137 140 16 Society of Automotive Engineers Inc Class B data communications Network messages part 4 Message definitions for three byte headers SAE J2178 4 FEB95 SAE Diagnostics for Light and Medium Duty Vehicles Standard Manual Warrendale PA 1997 pp 137 140 17 Society of Automotive Engineers Inc Table 6 The sixteen message Types SAE Diagnostics for Light and Medium Duty Vehicles Standard Manual Warrendale PA 1997 pp 112 18 Society of Automotive Engineers Inc Class B data communications Network messages Detailed header format and Physical Address Assignments SAE J2178 1 Jan95 Diagnostics for Light and Medium Duty Vehicles Standard Manual Warrendale PA 1997 pp 109 115 19 Society of Automotive Engineers Inc Class B data communications Network messages Data Parameter Definitions SAE J2178 2 Jan95 Diagnostics for Light and Medium Duty Vehicles Standard Manual Warrendale PA 1997 pp 116 136 20 Society of Automotive Engineers Inc E E diagnostic test modes SAE 1979 Jul96 Diagnostics for Light and Medium Duty Vehicles Standard Manual Warrendale PA 1997 pp 29 38 21 Society of Automotive Engineers Inc
42. f stored emission related power train trouble codes from all the modules that have this available Then send a mode 03 request for all the stored emission related power train codes Each module that has codes stored will respond with one or more 47 messages each containing up to 3 codes If no codes are stored in the module then the module may not respond to the request The diagnostic trouble code consists of an alphanumeric designator BO B3 for Body C0 C3 for Chassis PO P3 for power train and U0 U3 for network communication followed by three digits The assignment of proper alphanumeric designator should be determined by the controller into which a particular function is being diagnosed is being integrated In most cases the alphanumeric designator will be implied since diagnostic information will be requested from a particular controller 21 The diagnostic trouble codes are transmitted in two bytes of information for each code The first two bytes high order of the first byte for each code will be zeros in case of power train code The second two bits will indicate the first digit of the diagnostic code 0 through 3 The second nibble of the first byte and the entire second byte are the next 3 digits of the actual code If less than three trouble codes are reported the response bytes are padded with 00 to fill the 7 data bytes If no DTC s are reported the response is allowed but not required The interpretation of diagnostic trouble
43. function still very close to 1 5 times 20 the standard but without the MIL illuminating below the emission standards on some vehicles A provision was provided in the OBD II regulation to allow with Executive Officer approval manufacturers to use the Unified Cycle as an option to the FTP cycle for demonstration of monitoring system performance The Unified Cycle was developed by the ARB to represent real world driving and quantify in use vehicle emission levels This provision would allow manufacturers greater flexibility in designing monitoring strategies without diminishing the frequency with which the monitor executes during typical driving Because this flexibility may be useful for other monitoring requirements the provision would not be limited to just catalyst monitoring Manufacturers demonstrating a specific need for a particular monitor would be allowed to use the Unified Cycle for demonstration and monitoring purposes 2 52 Misfire monitoring The OBD II requirements presently include monitoring for proper combustion in each engine cylinder to ensure that misfiring does not contribute either to excess emissions or to catalyst damage because of overheating The OBD II system has to identify the cylinder or cylinders that are misfiring under most conditions During the initial phase in of OBD II requirements for 1994 through 1996 models manufacturers were only required to monitor for misfire over the engine operating conditions enc
44. g in urban areas state and national regulatory agencies are passing more stringent automobile emission standards California is the first state to take serious action with regard to automobile emissions and fuel consumption The California Code of Regulations CCR has developed an enhanced inspection and maintenance I amp M program commonly referred to as smog check II that was to be implemented in the1996 calendar year All 1996 and later model year passenger cars light and medium duty trucks sold in California have to be equipped with an On Board Diagnostic OBD II system The EPA Environmental Protection Agency updated the California OBD II requirements for federal OBD II compliance demonstration This system is designed to monitor critical emission related components and activate a MIL Malfunction Indicator Light when a failure or a drift in calibration is likely to cause emissions to exceed 1 5 times the vehicle certification standards 1 With the increasingly complex electronic systems on new vehicles it is becoming more difficult to repair and maintain the vehicles Therefore the SAE Vehicle E E System Diagnostic committee was formed to increase customer satisfaction and lower product life cycle costs by investigating and recommending standards that will more effectively diagnosis vehicle electrical and electronic system problems The OBD II regulations define diagnostic functions to be supported by the vehicle and functions t
45. gen storage can be used as an indicator of catalyst performance discriminating between catalysts with sufficient and insufficient oxygen storage capability In addition to being used for catalyst monitoring the rear sensor can be used to monitor and correct for front oxygen sensor aging as needed to maintain the stochiometric air fuel mixture at high mileage With a properly functioning catalyst the rear oxygen sensor signal will be fairly steady since the fluctuating oxygen concentration due to the fuel system cycling about stoichiometric at the inlet of the catalyst is damped by the storage and release of oxygen in the catalyst When a catalyst deteriorates damping is reduced causing the frequency and peak to peak voltage of the rear oxygen sensor to approximate the signal from the oxygen sensor before the catalyst The OBD II regulation currently requires manufacturers to identify a malfunction on low emission vehicles when the catalyst system has deteriorated to the point that tailpipe emissions exceed 1 5 times the applicable HC standard Manufacturers are required to phase in use of this malfunction criterion for low emission vehicles on 30 19 percent of the 1998 model year vehicles 60 percent of the 1999 model year vehicles and 100 percent of the 2000 model year vehicles Most manufacturers have worked to develop strategies that monitor the oxygen storage capability of the front portion of the catalyst system Factors that manufacturers
46. iagnostic OBD II system In addition to the functions of Universal scan tool this system should be able to interface with the PC so that the required data can be captured and used for future reference The data transfer should enable the transfer of both the stored data in the tester and the real time data when the engine is running to the PC This stored data can be used to build a database for all the cars in Texas when they are operating correctly and when there is a problem This stored data can then be retrieved to compare with current data from the vehicle during the inspection and testing With the interface of this system to the internal network supported by TMCP Texas Motorist s Choice Emissions the Texas government can implement it as a part of state s vehicle emissions testing program The OBD II Scan tool is any test equipment that meets the requirements of the SAE J1978 JUN 94 document 4 The OBD II scan tool can be divided into three parts the Physical layer the Data link layer and the Application layer Various layers of implementation are shown in Figure 1 1 The application and data link layers are software part of the project and Physical layer is the hardware part Each layer is described in Chapter 3 Application Layer Data link Layer Physical Layer Figure 1 1 Basic Block Diagram of Scan Tool The OBD II scan tool must be able to communicate with the vehicle control modules using the prescribed commun
47. ication interfaces There are three types of communication interfaces that are used to access the OBD II functions for a given vehicle but only one is allowed in any one vehicle The interfaces are 1 SAE J1850 41 6 Kbps PWM 2 SAE J1850 10 4 Kbps VPW and 3 ISO 9141 2 In this project only two protocols SAE J1850 41 6 Kbps PWM SAE J1850 10 4 Kbps have been implemented The aim of this thesis is to develop a PC based universal on board diagnostic scan tool which can be used to test any vehicle which supports OBD II The test equipment must also be able to store diagnostic data for further reference and records and interface to other PC programs The basic functions which the OBD II scan tool is required to support or provide include e Automatic hands off determination of the communication interfaced used e Obtaining and displaying the status and results of vehicle on board diagnostic evaluations e Obtaining and displaying OBD II emission related diagnostic trouble codes as defined in SAE J2012 JUL 96 e Obtaining and displaying OBD II emission related current data e Obtaining and displaying OBD II emissions related freeze frame data e Clearing the storage of OBD II emissions related diagnostic trouble codes OBD II emissions related freeze frame data storage and OBD II emissions related diagnostics test status e Obtaining and displaying OBD II emissions related test parameters and results as described as described in SAE J1
48. ion and that any user may be liable for copyright infringement Agree Permission is granted 02 04 1999 Student s Signature Date Disagree Permission is not granted Student s Signature Date
49. ions related current data and freeze frame data items their parameter Ids data resolution and data conversion information units and display formats is provided in SAE J1979 20 The display units shall be the Standard International SI and English units as specified in SAE J1979 20 The display of each OBD II emissions related current data or freeze frame data should include the following 1 Data value 2 Data Parameter id or name 3 The module id of the module that supplied the data As a minimum the data values of two data items must be displayed simultaneously A display of the parameter Ids of the data items and the Ids of the modules that supplied the data items must be easily accessible if not displayed with the data values The units of measure associated with the data items displayed must either be displayed with the data values easily accessible on another display or otherwise readily available to the user e g on the tester body as a part of the tester on a cheat sheet etc Having this information available in a user s manual separate from the body of the tool 44 does not satisfy this requirement The display must be capable of showing alphanumeric characters 5 2 User Input The OBD II Scan Tool must include some form of user input that would allow the user to a Select between the basic functions required by OBD II i e display current data display freeze frame data display trouble codes clear e
50. ission related Diagnostic information sied cova se iaeoa EE ECR ia 49 5 4 5 Mode 05 Request Oxygen Sensor Monitoring Test results 49 5 4 6 Mode 06 Request On Board Monitoring Test results for non continuously monitored System 0 0 0 00 0000 50 5 4 7 Mode 07 Request On Board Monitoring Test results for continuously monitored System 0 00 0 cece cece cece ees 50 5 4 8 Mode 08 Request control of On Board System ESCOCIA ot tna 50 5 5 Multiple Response to a Single Data Regest sisse pet iet o 5 2 0 Response LIME areae tuf tl eet tait tu eR E Mte AE EM 5 5 7 Minimum Time between Requests from Scan TOOL 52 5 8 Data Not Avalable e di Ea 52 3 9 Maximum Y AU a Da t uibus e Kod 52 6 SOFTWARE IMPLEMENTATION iere E e TE 53 A T E casetas 53 6 2 Diagnostic Message Format 0 0 0 0 0 0 0 0000 cece cece e 53 09 Response Message a emu Orge ct de taeda he PIRENEA 55 GOA Request MessaBe s ses aroha a TOR SL aM oa 57 65 Standard DISPO E AN 59 TRESUETS curtir laca 64 7 1 Display of diagnostic trouble COAES ooooooococcoccocccccocccoroncco eee eens 64 7 2 Freeze Frame Data DISplay subes as e e eb ERE QE E 65 TEPC MECE cout erus De UD wie ed tnum E RE de 69 S CONCEUSIONS iia naaa aeia ica 72 8 1 Recommendations for Future Work 00 00 ccc 73 BIBLIOGRAPHY edite ee Daneel rete slate tae A Seta 74 APPENDIX SOURCE CODE FOR THE APPLICATION LAYER AND DATA LINK A A O A et e
51. lement and Structure ssis sss sse 33 4 4Class B Data Communication Network Message 0000 0 000 33 4S Header Ereld A A hehe on Ou o Rune ya tece tea bates 34 4 5 1 Single Byte Header Message Format ssuousuuuuuuuss 35 4 5 2 Consolidate Header Message Format susuuuuLuuus 36 4 5 2 1 One Byte Form of consolidate Header Format 36 4 5 2 2 Three Byte form of the consolidate header format 36 4 5 3 Target Address Byte ete t Le E nete NEG Ie agamus 38 iv SA A ee 38 A A O tata oe ednesan neem 39 4 6 1 Functional Data Field Formats sse 39 4 6 1 1 Functional Data Field Format 081 39 4 6 1 2 Functional Data Field Format 2 ssseeeeeeess 40 4 6 1 3 Functional Data Field Format 3 aesir rrer 40 4 6 1 4 Functional Data Field Format 4 sss 41 4 7 In Frame Response TER ooooooooococcccccoccoccccoconccco cnn narcos 41 4 8 Cyclic Redundancy Check CRC sss 42 5 STANDARD DISPLAY FORMAT aeaee raserer renees rr 44 5 1 General Characteristics Display 0 00 cece cece cece cence 44 NA 45 23 Application laten 45 SS Fes MOIES A a 46 5 4 1 Mode 01 Request Current Power Diagnostic Data 46 5 4 2 Mode 02 Request Powertrain Freeze Frame Data 47 5 4 3 Mode 03 Requested emission related Powertrain Diagnostic Trouble Codes c de n e eid 47 5 4 4 Mode 04 Reset clear em
52. lled in the above programs f SN include lt stdio h gt include lt stdlib h gt table of crcs of all 8 bit messages unsigned char crc_table 256 check if the table is computed or not int crc_computed 0 int n c unsigned char new_crc unsigned char crc unsigned char buf int len void makecrc unsigned char crc unsigned char buf int len void main j make a crc table for fast computation void makecrc int n k c for n 0 n lt 256 n c n for k 0 k lt 8 k if c amp 1 c 0X1ld c gt 1 85 else c c gt gt 1 j crc table n unsigned char c j crc computed 1 The crc is initialized to all 1 s and the transmitted value is the 1 s complement of the final running crc unsigned char new_crc unsigned char crc unsigned char buf int len unsigned char c crc int n if lcrc_computed makecrc for n 0 n lt len n j return c c crc table c buf n amp OXff c gt gt 8 y unsigned char crc unsigned char buf int len return new_crc OXff buf len OXIE 86 Eee AAA This part of the program provides the interface between the data link layer and the Application layer a RRR RR RRR KKK KKK KKK KK KKK KKK RRR KK RR KKK RAK KR KKK KKK RK EK RK KEK KKK RK KK include lt windows h gt include datalink h BOOL WINAPI DLLMain HINSTANCE hDLL DWORD dwReason LPV
53. lue As Single Dim 1 As Byte Dim Step As Integer If Response 1 lt gt amp H45 Then Debug Print RESPONSE ERROR Else Select Case Response 2 Case amp H1 To amp H9 For1 0To7 If Response 3 2 1 Then Label2 0 Caption O2 Sensor Location amp SensorLab I Use the selected sensor directly Label2 0 Caption O2 Sensor Location amp SensorLab SensorLoc Exit For End If Next i Value Calculation CLng Response 4 Response 2 txtO2SensorData Response 2 Text Value End Select End If End Sub Private Function Calculation DataIn As Long Index As Byte As Single Dim Min amp H1 To amp H9 As Single Dim Scaling amp H1 To amp H9 As Single 101 Dim Max amp H1 To amp H9 As Single Dim J As Integer MIN ARRAY amp Scaling Array For J amp H1 To amp H9 Min J 0 Min Array Scaling J 0 005 Scaling Array Next J Scaling 5 0 004 Scaling 6 0 004 Scaling 9 0 04 MAX ARRAY Calculation Min Index Scaling Index Dataln End Function Private Sub Form_Load Dimi As Integer set all disabled and invisible first Fori 0To 9 Label2 1 Enabled False txt02SensorData 1 Visible False Next 1 then recover those selected PID Label2 0 Enabled True For i 0 To 99 If TestID 1 0 Then Exit For Else Label2 TestID 1 Enabled True txtO2SensorData TestID i Visible True End If Next 1 End Sub Private Sub Timerl Timer Static pointer As Integer pointer pointer
54. make This helps the service technician to maintain only one test equipment to test all the vehicles he or she repairs The results shown in Chapter 7 are verified using a Vetronix Mastertech 26 scan tool on the 1996 and 1997 model vehicles The diagnostic trouble code displayed on the Vertronix Mastertech by actually removing the fuel injector from the cyclinder 5 in the vehicle is the same as that displayed by the system developed in this project when appropriate input is given as described in Chapter 7 So the Universal scan tool developed in this project can effectively detect any emission related malfunctions As the Universal scan tool developed in this project is a PC based scan tool it is relatively easy to store the retrieved data from the vehicle and to transmit this data to the TX96 equipment for communication with the Texas Data Link system compared to normal scan tools 72 8 1 Recommendations for Future Work The results obtained show that there is definite room for improvements in the Universal scan tool One of the areas of future work can be to implement the enhanced diagnostic test modes 23 The enhanced diagnostic test modes can supplement the legislated diagnostic test modes defined in SAE J 1979 20 These modes increase the access to emission related test data compared to diagnostic test modes included in SAE J 1979 20 and can also obtain non emission related data Implementation of enhanced diagnostic test codes
55. may require a single level topology to be implemented using multiple interconnecting cables operating in various modes active or passive However the requirement to use multiple buses for redundancy purposes does not change the single level bus topology definition if the following criteria are maintained 1 All nodes devices transmit and receive from a single path 2 All nodes devices receive all frames at the same time 3 Communication on each data bus is identical 26 3 2 3 Data Bus Control Although various methods of data bus control can be used this Class B network is intended for masterless bus control The principal advantage of the masterless bus control concept is its ability to provide the basis for an open architecture data communications system Since a master does not exist each node has an equal opportunity to initiate a data transmission once an idle bus has been detected However not all nodes and or data are of equal importance prioritization of frames is allowed and the highest priority frame will always be completed This also implies that frame data contention will not result in lost data Two disadvantages of the masterless bus concept are that the data latency cannot be guaranteed except for the single highest system priority frame and bus utilization extremes are difficult to evaluate 11 3 3 ISO 9141 2 1994 E Road Vehicles Diagnostic Systems CRAB Requirements for Interchange of Digital Information
56. missions related data and display test parameters and results b Select for simultaneous display at least two items of any one of the following 1 2 3 4 OBD II emissions related current data OBD II emissions related diagnostic trouble codes OBD II emissions freeze frame data OBD II emissions related test parameters and results c Verify a request to clear and or reset OBD II emissions related diagnostic information as defined by SAE J1979 d Enter and send Expanded Diagnostic Protocol messages 5 3 Application layer The Application layer implements the General characteristic display described above This layer establishes the relationship between the application input and output devices including what is expected of human operators This layer documents the high label description of the function including control algorithms if appropriate Application 45 layer implements the standard format of the data to be displayed 22 The various modes described below help in analyzing the request and response messages and their operation The higher layer Application layer sends a request message for a particular information and gets the information from that particular node in the vehicle as response message 5 4 Test Modes 5 4 1 Mode 01 Request Current Power Diagnostic Data The purpose of this mode is to allow access to current emission related data values including analog inputs and outputs and sy
57. mportant environmental achievements of the last quarter century 8 2 3 1 Clean air act The Clean Air Act of 1970 set a national goal of clean air for all It established the first specific responsibilities for government and private industry to reduce emissions from vehicles factories and other pollution sources In many ways the far reaching law has been a great success Today s cars for example typically emit 70 to 90 percent less pollution over their lifetimes than their 1970 counterparts In 1990 Congress and the Administration amended and updated the Clean Air Act for the first time since 1977 considering the new pollution sources and unrecognized threats such as global warming acid rain and air toxins The new Clean Air Act strengthens components of the earlier law The tailpipe standards for cars buses and trucks have been tightened and Inspection and Maintenance I amp M programs have been expanded to include more areas and allow for more stringent tests 9 The 1990 law also introduces several entirely new concepts with regard to reducing motor vehicle related air pollution like alternative fuels For the first time fuel is considered along with vehicle technology as a potential source of emission reductions And more attention is focused on reducing the growth in vehicle travel The Inspection and Maintenance I amp M program is made more stringent by including on board diagnostics The EPA published a final rule 61 FR 45
58. nal service provided by the Data Link Layer is error checking When error are detected they may be corrected or higher layers may be notified 29 3 3 3 Physical Layer The Physical Layer and its associated wiring form the interconnecting path for information transfer between Data Link Layers Typical Layer protocol elements include voltage and current levels media impedance and bit symbol definition and timing 14 30 Standard Message Application Layer Hardware or Software As Needed Data Link Layer Bit Byte or message level Non Destructive Determined by message Idle Bus Detection Bit level synchronization 12 Bytes Most Significant First U 9 lt 2 Q E A E Ez O S o E O un Un QO H J Sp S trj o J 5 s ai o n gt gt Invalid bit CRC Structure Ignore Message No IFR CRC 10 4 Kbps 41 6Kbps Physical Layer Dual wire Figure 3 2 Map of SAE J1850 to the ISO Model 31 CHAPTER 4 DATA LINK LAYER 4 1 Introduction The primary function of the Data Link Layer is to convert bits and symbols to validate error free frames The Data Link Layer deals with the following attributes 1 Addressing Strategy 2 Network Access and Data Synchronization 3 Frame Element and Structure 4 Error Detection 5 Error Response 4 2 Addressing Strategy Two types of addressing strategies are defined and can co exist on this n
59. nditions for which data is not available One condition is that the test mode is not supported and the other condition is that the test mode is supported but the data is not currently available 5 9 Maximum Values If the data value exceeds the maximum value possible to be sent the on board system should send a maximum message value possible FF or SFFFF The tool should display the maximum value or an indication of data too high This is not normally critical for real time but essential in case of misfire at 260 Km h with resulting freeze frame data stored 52 CHAPTER 6 SOFTWARE IMPLEMENTATION 6 1 Introduction In the previous chapters various addressing modes test modes and the frame structures were described in detail This chapter gives a detailed description of how the data link and Application layers are implemented in this project It gives a detailed description of all the flow charts designed to implement the data link layer using a C source code and Application layer using the visual basic software This chapter also includes the message format which was comprehended for the Chapters 4 and 5 to implement a Universal scan tool 6 2 Diagnostic Message Format The message format used in implementing the data link layer is described below Functional addressing is used for all generic diagnostic test modes because the test tool does not know which system on the vehicle has the information that is needed The maxim
60. ng additional information an on board diagnostic system can be developed to monitor the entire emission control system When a malfunction is detected the on board diagnostic system notifies the driver by illuminating a Malfunction Indication Light MIL on the instrument panel A code identifying the likely area of the malfunction is also stored in memory On board diagnostic regulations were originally adopted in California in 1985 for 1988 and later light and medium duty vehicles equipped with three way catalysts and feedback fuel control systems This regulation is now known as OBD I and was developed because the increasing use of sophisticated electronic emission and power train control systems made it increasingly difficult for technicians to detect defective 8 components OBD I was seen as a promising mechanism for quickly identifying faulty electronic based emission control system components in California s Smog Check Program In OBD II the ARB Air Resources Board broadened the scope of OBD I by increasing the number of components and systems to be monitored by the system When OBD I was adopted technology did not exist or had not been identified to monitor some of the components now contained in OBD II such as the catalyst and evaporative control system monitoring OBD II requires that virtually every emission control system and electronic emission related power train component be monitored In addition to the foregoing OBD II
61. o be supported by the test equipment that interfaces with the vehicle diagnostic functions Ranges of test equipment from a handheld scan tool to a PC based diagnostic computer can be used to perform the required interface support function 1 2 Diagnostic tool Maintaining the microprocessor equipped car is made easier because the ECM Electronic Control Module through the OBD II standards aids in maintenance by telling or at least giving a good hint the automobile mechanic what is wrong with the car Before scan tools to read the OBD II data were built many crude methods were implemented to find the fault when the MIL was illuminated One of the methods of detecting a problem is by simply connecting two pins in the under dash diagnostic connector which puts the EMC in the in service mode Then the MIL blinks at a rate that can be referenced to the error the controller found For instance a malfunctioning exhaust gas recirculation valve EGR give a trouble code 32 and the MIL starts to blink in a flash flash flash pause flash flash rate To know the malfunction the user has to refer to a huge manual which describes how to interpret the code 2 In another method a normal PC is connected a to the diagnostic connector and the PC runs special written diagnostic software The PC then communicates with the on board computer and depending on the model and type of the car computer the PC can capture records in a rate varying from one per two
62. odifications to strengthen the tank walls to resolve false malfunction detection concerns 2 5 4 Positive Crankcase Ventilation PCV System Monitoring Currently the OBD II regulation does not contain specific monitoring requirements for the detection of PCV system failures Additionally monitoring of the PCV system is not required under the comprehensive component monitoring section of the regulation because such systems generally do not use electronic components Nonetheless certain failure modes of the PCV system can cause a substantial increase in emissions by venting crankcase hydrocarbon emissions directly to the atmosphere To 23 take care of these excess in use emissions a PCV system monitoring requirement is added to the OBD II regulation Drawing air and fuel into the cylinder compressing the mixture with a piston and then igniting the mixture achieve combustion in each of the cylinder After the combustion event the mixture is exhausted from the cylinder with another stroke of the piston However during the combustion process exhaust gases can escape past the piston into the crankcase The PCV system is then used to remove these gases known as blow by from the crankcase and directs them to the intake manifold to be burned by the engine Before the introduction of PCV systems in the early 1960 s these vapors were vented to the atmosphere The U S EPA s Mobile5a emission model quantifies these emissions at 1 2 grams p
63. on secondary air systems fuel systems and all electronic power train components that can affect emissions when malfunctioning The regulation also requires OBD II systems to provide specific diagnostic information in a standardized format through a standardized serial data link on board the vehicle 6 Some amendments were made so that the U S EPA could also adopt the OBD II implemented by CCR The proposed amendments are to clarify the MIL illumination requirements for misfire detection and to avoid tempering resistance in the OBD II requirements 2 3 Environment Protection Agency EPA The mission of the U S Environmental Protection Agency is to protect human health and to safeguard the natural environment air water and land upon which life depends 7 Environmental protection is an integral consideration in U S policies concerning natural resources human health economic growth energy transportation agriculture industry and international trade and these factors are similarly considered in establishing environmental policy 7 In 1970 the nation passed the Clean Air Act in response to the growing recognition that our air was potentially unhealthy The Clean Air Act quickly eliminated the most egregious sources of air pollution In addition the law put in place health based standards to protect our right to breathe clean air All across the country improvement in 11 air quality is regarded as one of the most i
64. on light is commanded to be illuminated but is not the vehicle shall fail the on board diagnostic inspection 2 42 On board diagnostics test report The results of the inspection or the test report after a vehicle is inspected is interpreted in the following ways 1 A motorist whose vehicle fails the on board diagnostic test shall be provided with On board diagnostic test results including the codes retrieved the status of the MIL illumination command and the customer alert statement 2 Ifany of the OBD codes are retrieved the corresponding component shall be listed on the test report as described in Table 2 2 Table 2 2 Listing of OBD Codes when Retrieved P0500 amp P0501 Vehicle speed sensor P0742 amp Torque Converter Clutch System P0743 amp P0744 17 3 In addition to any codes that are retrieved the test report shall include the following language Your vehicle s computerized self diagnostic system OBD registered the fault s listed below This fault s is probably an indication of malfunction of an emission component However multiple and or seemingly unrelated faults may be an indication of an emission related problem that occurred previously but upon further evaluation by the OBD system was determined only to be temporary Therefore proper diagnosis by a qualified technician is required to positively identify the source of any emission related problem 2 4 3 On board diagnostics test equipment r
65. ountered during the FTP test Beginning with the 1997 models however all but small volume manufacturers are required to phase in misfire detection over nearly the 21 entire engine operating range Misfire causing catalyst damage will generally be detected in less than a minute and lower levels of misfire will still be detected within two trips Sometimes misfires can occur temporary due to poor fuel quality unusual ambient conditions or other causes So the current OBD II MIL illumination requirements may need some revision to delay illuminating the MIL until misfire is more repeatable than under the current requirements The primary misfire patterns for which detection is most important are random misfire single cylinder continuous misfire and paired cylinder misfire 2 5 3 Evaporative System Monitoring The OBD II regulation requires manufacturers through the 1999 model vear to monitor the evaporative system for leaks equal or greater in magnitude than a 0 040 inch diameter hole With the 2000 model year manufacturers must begin to phase in monitoring for small leaks equal or greater in magnitude than a 0 020 inch diameter hole The requirements were developed in response to data indicating that small system leaks can cause evaporative emissions to exceed 30 grams per test over 15 times the standard on the 105 degree Fahrenheit test procedure An OBD II system shall monitor the proper operation of the evaporative system by checking
66. power enrichment deceleration enleanment FuelSystemStatus 3 Close Loop but fault with at least one oxygen sensor maybe using single oxygen sensor for fuel control FuelSystemStatus 4 FuelSystemStatus 5 FuelSystemStatus 6 FuelSystemStatus 7 Define the Secondary Air Status Dim AirStatus 0 To 7 As String AirStatus 0 upstream of first catalytic converter AirStatus 1 downstream of first catalytic converter inlet AirStatus 2 atmosphere off AirStatus 3 AirStatus 4 AirStatus 5 AirStatus 6 AirStatus 7 88 Define the Aux Input Status Dim AUX 0 To 7 As String AUX 0 Power Take_OFF Not Active AUX 1 Power Take OFF Active Dim Value As Single Dim I As Byte Dim Step As Integer Response 1 testmode 2 TestID 3 data_HighByte 4 data_LowByte If Response 1 lt gt amp H41 Then Debug Print RESPONSE ERROR Else Select Case Response 2 Case amp H3 For l 0 To 7 If Response 3 2 T Then txtCurrentData 2 Text FuelSystemStatus 1 Exit For End If Next I If Response 4 lt gt 0 Then ForI 0 To7 If Response 4 2 T Then txtCurrentData 3 Text FuelSystemStatus I Exit For End If Next I End If Case amp H4 To amp HB amp HD To amp HF amp H11 Value Calculation CLng Response 3 Response 2 txtCurrentData Response 2 Text Value Case amp HC amp H10 Dim Datalnput As Long DataInput CLng Response 3 256
67. r those selected PID For i 0 To 99 If PID2 i 0 Then Exit For Else Label2 PID2 1 2 Enabled True txtCurrentData PID2 1 2 Visible True End If Next i If PID2 0 3 Then PID 3 show the 2 fuel system status Label2 0 Enabled True txtCurrentData 0 Visible True End If End Sub Private Sub Timerl Timer Static pointer As Integer pointer pointer 1 Const maxium 10 If pointer gt maxium Then pointer 1 End If Response 1 amp H42 Response 2 pointer 3 Response 3 amp H1 Response 4 amp H33 Call Form_Activate For the true call to OBDII 99 Static 1 As Integer 1 1 1 If 1 gt PID2SelNum Then 1 0 reset PID2 counter if bigger than selected TestID Num End If Request 1 amp H2 Request 2 PID2 i For J 3 To 7 Request J 0 Next J Dim reply As Byte reply SendRequest Request 1 Response 1 Call Form_Activate End Sub 100 This code can display the Oxygen sensor data Private Sub emdCancel_Click Unload Me End Sub Private Sub F orm_Activate Define Sensor Location Marks Dim SensorLab 0 To 7 As String SensorLab 0 Bank1 Sensor SensorLab 1 Bank1 Sensor2 SensorLab 2 Bank1 Sensor3 SensorLab 3 Bank1 Sensor4 SensorLab 4 Bank2 Sensor1 SensorLab 5 Bank2 Sensor2 SensorLab 6 Bank2 Sensor3 SensorLab 7 Bank2 Sensor4 Response 1 testmode 2 TestID 3 Sensor_Location 4 data HighByte Dim Va
68. rivate Sub Form_Load End Sub This code is to request status of DTC Private Sub Optionl Click Index As Integer Label3 Visible True txtDTC 0 Visible True txtRemarks 0 Visible True txtDTC 0 SetFocus End Sub Private Sub cmdOK_Click Dim Mode PID As String Mode 17 Select Case True Case Option1 0 Value SendRequest Mode Case Optionl 1 Value PID 00 00 105 SendRequest Mode PID Case Option1 2 Value PID 40 00 SendRequest Mode PID Case Option1 3 Value PID 80 00 SendRequest Mode PID Case Option1 4 Value If txtDTC 0 Text Then MsgBox Input the DTC please Else convert the string to PID SendRequest Mode PID End If End Select End Sub This code is to clear DTC Private Sub cmdSearch Click If Option1 4 Value False Then MsgBox Click the OK Button to Clear please Exit Sub ElseIf txtDTC 0 Then MsgBox Please Input the DTC you want to Clear Exit Sub Else datDTCs Recordset FindFirst DTC amp txtDTC 0 amp txtRemarks 0 Text datDTCs Recordset Fields 1 Value Exit Sub End If End Sub Private Sub Form_Load End Sub Private Sub Optionl Click Index As Integer Label3 Visible True txtDTC 0 Visible True txtRemarks 0 Visible True txtDTC 0 SetFocus End Sub 106 This code is used to select the Freeze PID Private Sub cmdBack Click End Sub Private Sub cmdCancel Click Unload Me End Sub
69. s 6 5 and 6 6 give a description of how the diagnostic trouble codes and the current data from the automobile are displayed on the scan tool Detect OBDII Interface OBDII Main Function Select Window Readiness Clear Test Data Current Oxygen Data Sensors Freeze Frame Data Figure 6 3 Flowchart of Application layer 60 Readiness Test Select test items windows Yes Decode Response Selection Show Readiness Correct Test Results Encode Request Data Link Layer Function SendRequest Figure 6 4 Description of the Readiness Test 61 Show DTCs and Descriptions Show RetrievingDTCs Looks for DTC Database for Descriptions Decode Response Encode Request Data Link Layer Function SendRequest Figure 6 5 Display of Diagnostic Trouble codes 62 No Current Data Select data item windows Selection Show Current Correct Data Values Update Request Encode Request Decode Response Data Link Layer Function SendRequest Figure 6 6 Display of Current Data Form 63 CHAPTER 7 RESULTS The previous chapters detail the various aspects of the data link and Application layers This chapter summarizes the results and gives some future directions to make this system more versatile 7 1 Display of diagnostic trouble codes One of the most important functions of OBD II scan tool is to obtain and display OBD II emission related diagnostic trouble
70. s define whether additional data is used by that message 4 6 1 3 Functional Data Field Format 3 The data field format 3 message depending on the primary and secondary ID also has an extended address byte The extended address byte is used to determine where geographically on a vehicle a particular function is located 40 4 6 1 4 Functional Data Field Format 4 The data field format 4 message contains a byte which defines the diagnostic test mode of the target function being addressed The test mode byte is used to determine which diagnostic function is involved 18 19 4 7 In Frame Response IFR For In Frame Response the response byte s are transmitted by the responders and begin after EOD If the first bit of the in frame response byte does not occur at this point and the bus remains passive for a period of time defined as EOF then the originator and all receivers must consider the frame complete In frame response bytes may take one of the following forms 1 None 2 A single byte transmitted from a single recipient typically a unique identifier ID or address 3 Multiple bytes with a single byte transmitted from each recipient The effect is to concatenate the individual response bytes into a response stream The response byte from each recipient must be unique typically a physical address ID n Arbitration takes place during the response process so that each recipient if arbitration is lost during its re
71. seconds up to 20 records per second These records contain momentary data fields filled by information on all the sensors and 2 actuators on the car The data can be to logged and graphed for future use The data is a very valuable aid in trouble shooting and trend tracking However most of the PC programs available can only be used with a specific make of automobile they are not universal 2 To avoid these inconveniences of counting the number of times the MIL blinks or connecting a PC to the diagnostic connector small hand held tools were developed These small hand held tools when connected to the diagnostic connector to display the diagnostic trouble code which consists of an alphanumeric designator followed by three digits These primitive scan tools could not describe the diagnostic trouble code consequently ordinary people could not figure out the problem without consulting the thick manual Scan tools designed in the early days could support only few makes and models of automobiles Therefore the service technician was supposed to possess a specific scan tool for each vehicle he repaired from a different manufacturer As a result there was a risks of a new monopoly of maintenance and repair by manufacturer approved dealerships This would severely limit the freedom of choice of consumers There could be a sharp increase in the cost of vehicle maintenance and repair Roadside rescue organization and independent garages would be unabl
72. shown in Figure 4 31 This allows up to 256 message identifiers 15 sup TT EI Message ID 256 Figure 4 3 Single Byte Header Format 35 4 5 2 Consolidate Header Message Format The consolidate header format includes both a one byte form and a three byte form 4 5 2 1 One byte Form of consolidate Header Format The one byte form utilizes 7 bits from the message identifier resulting in 128 distinct Ids The H bit is always at logic one 15 The one byte form of the consolidate header is shown in Figure 4 4 wer PE PPP Wemem m O Message ID 128 Figure 4 4 One Byte Form of Consolidate Header 4 5 2 2 Three byte form of the consolidate header format The header byte utilizes the first three bytes of the message The H bit of the first byte is always at logic 0 The remaining seven bits of the first byte contain information about priority PPP and message type KYZZ The second byte contains the target address information The target can either be functionally addressed or physically addressed The third byte contains the physical address of the source of the message The three byte header is described in detail in Figure 4 5 and Table 4 1 36 Figure 4 5 Three Byte form of Consolidate Header Table 4 1 Description of Byte 1 of Three Byte Consolidate Header a Priority 0 to 7 i K IN FRAME RESPONSE IFR IFR required Fr IFR Not allowed Y 0 Addressing Mode 0 Func
73. sponse byte will retransmit the single byte until the recipient observes its unique byte in the response stream Once a given recipient observes its own unique response byte it discontinues the transmission process to allow any remaining responders to transmit their byte 4 4 One or more data bytes all from a single recipient A CRC byte may be appended to the data byte s Even 1f In frame response bytes are used the overall frame message length limit remains in effect The sum total of data bytes CRC bytes and in frame response bytes shall not exceed the frame length The maximum number of message bytes in a frame ie excluding frame delimiters SOF EOD EOF and IFS is 12 bytes 18 4 8 Cyclic Redundancy Check CRC The CRC is required with either of the header byte systems used The method of calculating and checking the CRC byte is defined as follows An invalid CRC byte may constitute a detected error 1 The CRC calculation and the CRC checker shift registers or memory locations will be located in the sender and receiver nodes respectively and shall be initially set to the all ones state during SOF The setting to ones prevents an all zeros CRC byte with an all zero data stream 2 All frame bits that occur after SOF and before the CRC field are used to form the Data Segment Polynomial which is designated as D X For any given frame this number can be interpreted as an n bit binary cons
74. stem status information The request for information includes a parametric Identification PID that indicates the on board system the specific information requested The on board system will respond to this message by transmitting the requested data value last determined by the system All the data values returned from the sensor readings will be actual reading Not all PIDs are applicable or supported by all systems PID 00 is a bit encoded PID that indicates for each module which PIDs that module supports PID 00 must be supported by all modules that respond to 01 request that determines which protocol is supported for OBD II communications The message data byte is given in Table 5 1 46 Table 5 1 Message Data Bytes Data Bytes 5 4 2 Mode 02 Request Power train Freeze Frame Data The purpose of this mode is to allow access to emission related data values which were stored during the freeze frame required by OBD II regulations PID 02 is the DTC that caused the freeze frame data to be stored If freeze frame data is not stored in the module the system should report 00 00 as the DTC Any data reported when the stored DTC is 00 00 may not be valid 5 4 3 Mode 03 Requested emission related Power train Diagnostic Trouble Codes The purpose of this mode is to enable the off board test device to store emission related power codes This is achieved by first sending Mode 01 PID 01 request to get the number o
75. systems also require the detection of engine misfire The underlying principle behind OBD II is that most malfunctions should be detected when the performance of a component or system deteriorates to the point that the vehicle s emissions exceed a threshold value tied to the applicable emission standard This is in contrast to detecting malfunctions when the component or system is simply no longer functioning Under the OBD II approach the vehicle operator is notified at the time the vehicle begins to marginally exceed emission standards The regulation as adopted is specific regarding when the vehicle operator must be notified via the MIL to ensure prompt notification In OBD IL the ARB Air Resources Board also required that additional information be provided to technicians for diagnosis and repair of emission related problems OBD II systems are required to use new standardized on board vehicle communication systems to provide service technicians with detailed information about system performance and detected malfunctions This information includes stored fault 9 codes that will lead technicians to the likely area of the malfunction and continuously updated information for some engine parameters to help them isolate the specific fault The communication systems are to provide all of this information in a standardized format through a communication link similar to a telephone line Specifications for this link have been developed by the Societ
76. t monitoring and the evaporative system monitoring 5 4 7 Mode 07 Request On Board Monitoring Test results for continuously monitored System The purpose of this test mode is to allow access to the results for on board diagnostic monitoring tests of specific components systems that are continuously monitored during normal driving conditions The intended use of this data is to assist the service technician after vehicle repair and after clearing diagnostic information by reporting test results after a single driving cycle If the tests failed during the driving cycle the DTC associated with the test will be reported If the tests indicate a failure after additional driving then the MIL will be illuminated and a DTC will be set and reported in mode 03 indicating a faulty component 5 4 8 Mode 08 Request control of On Board System Test or component The purpose of this test mode is to enable the off board test device to control the operation of an on board system test or component If any data bytes are unused for any test they should be filied with 00 to maintain a fixed length To obtain the information regarding the message data bytes of each mode and test ID and data byte description refer SAE J1979 20 Enhanced E E Diagnostic test modes are defined for access to emission related test data beyond what is included in SAE 56 31997 and for non emissionn related data These modes are not included here as thev these need not be
77. tant where n is equal to the frame length counted in bits 3 The CRC division polynomial is X X X X 1 This polynomial is designated as P X 4 The Remainder Polynomial R X is determined from the following Modulo 2 division equation 42 X D X X r XH X Q X ROO P X P X NOTE Q X is the quotient resulting from the division process 5 The CRC byte is made equal to R X where R X is the one s complement of R X 6 The Frame Polynomial M X that is transmitted is shown in Equation 2 7 M X X D X R X 8 The receiver checking process shifts the entire received frame including the transmitted CRC byte through the CRC checker circuit An error free frame will always result in the unique constant polynomial of X X X C4 hex in the checker shift register regardless of the frame content When a CRC field protects In Frame Response data the previous rules are used to define the CRC except that the sender and receiver nodes are interchanged The CRC calculation only includes the in frame response bytes Note that the SOF EOD EOF and NB are not used in the CRC calculation and serve as data delimiters 43 CHAPTER 5 STANDARD DISPLAY FORMAT 5 1 General Characteristics Display The OBD II Scan Tool must be capable of displaying simultaneously at least two items of OBD II emissions related current data items or OBD II emissions related diagnostic trouble codes A list of the OBD II emiss
78. the function of its electromechanical components and by checking the flow of hydrocarbon vapors from the canister to the engine Manufacturers are complying with the current leak detection requirements using monitoring techniques that create either a vacuum or a pressurized condition in the fuel tank and evaporative system The pressure inside the system is monitored over an interval of time If the pressure or vacuum 22 changes toward ambient at a significant rate a leak is considered to be present If the pressure or vacuum holds reasonably steady the system is considered leak free Manufacturers can be exempted from detecting small leak sizes if they provide sufficiently reliable data demonstrating that evaporative emissions will not exceed 1 5 times the applicable standards For those system designs for which a larger emission impact would result from small leaks the requirements would remain unchanged To meet the evaporative system requirements on some vehicles with specific types of fuel tank designs steel tanks can be replaced by plastic fuel tanks These tanks are generally more flexible than steel tanks possibly causing some slight deformation when pressure or vacuum is applied Although slight the manufacturers indicate that the deformation may change the pressure in the tank sufficiently to alter the results of the monitoring system and possibly cause false malfunction detections The manufacturers have stated that they are making m
79. tional addressing 00 Physical addressing ZZ Specific Message Type 01 Refer 17 The priority field is three bits in length and proceeds the header type H bit The priority bit assignments are manufacturer specific and are not assigned by SAE The 37 priority 0 is the highest level of priority and priority 7 111 is the lowest level of priority 4 5 3 Target Address Byte The second byte of the three byte form of the consolidate header format contains either a functional or a physical target address The physical and functional addresses are found in SAE J2178 4 16 The W bit in the target address byte differentiates between the command target and status target If W is 0 it signifies a Command target if 1 signifies a status target Figure 4 6 describes the target address mug opp r p rpg qe ge m Primary ID 128 pairs Figure 4 6 Target Address 4 5 4 Source address The third byte of the three byte format of the consolidate header format is the physical address of the message The physical assignments are available in SAE 32178 1 18 38 4 6 Data Field The data or the data field refer to a field within a frame that may include bytes with parameters pertaining to the message and or secondary ID and or extended addresses and or test modes which further define a particular message content being exchanged over the network In both message header formats
80. um message length effectively limits the number of bytes that can be used to 12 bytes To conform to the SAE J1850 11 limitations on message length a diagnostic message is selected to have a three byte header a maximum of seven data bytes a required ERR error detection byte and an in frame response byte as shown in Table 6 1 The first three bytes of all diagnostic messages are the header bytes The value of the first header byte is dependent on the bit rate of the data link and type of message The 53 second byte has a value that depends on the type of message either in a response or a request The third header byte is the physical address of the device sending the message The device address for OBD II scan tool is F1 Vehicle manufacturers do not use this format for any purpose other than diagnostic messages Table 6 1 Standard Diagnostic Message Format Header Bytes Hex EA AO VO EEE Priority Target Source 1 2 3 4 5 6 7 ERR IFR type Address Address Diagnostic Request at 10 4 Kps SAE J1850 and ISO 9141 2 68 6A rx Maxmum7DsaByes TO ye Tomo Diagnostic Response at 10 4 Kps SAE J1850 and ISO 9141 2 48 6B add Maximum7DaaBytes Yes mo Diagnostic Request at 41 6 Kps SAE J1850 Diagnostic Response at 41 6 Kps SAE J1850 4 6B add Maximum7DataByte Yes Yes The maximum numbers of available data bytes are seven The first data byte follo
81. ut Power Steering Pressure Sensor Circuit Intermittent Power Steering Pressure Sensor Circuit Intermittent System Voltage Malfunction System Voltage Unstable System Voltage Low System Voltage High Computer and output Circuits Codes Break Switch Input Malfunction Transmission Range Sensor Circuit Malfunction Transmission Range Sensor Circuit Range Performance Transmission Range Sensor Circuit Low Input Transmission Range Sensor Circuit High Input Transmission Range Sensor Circuit Intermittent Torque Converter Brake Switch B Circuit Low 14 soy Table 2 1 Continued Soe ewe 7 Torque Converter Brake Switch B Circuit High gt The list of codes shall be updated in conjugation with changes to section 40 CFR 86 094 17 h 3 of EPA 24 1 On board diagnostics test procedures The test sequence for the inspector of the on board diagnostics system on 1996 and newer light duty vehicles and light duty trucks shall consist the following steps l The on board diagnostic inspection shall be conducted with key on engine running KOER 2 The inspector shall locate the vehicle connector and plug the test system into the connector 3 The test system shall send a Mode 01 PID 01 request to determine the evaluation status of the vehicle s on board diagnostic system The test system shall determine what monitors are supported by the on board diagnostic system and the readin
82. wing the header is the test mode and the remaining 6 bytes vary depending on the specific test mode Each mode has a specific length determined by the parametric identification PID or Test ID or on the particular mode depending on a specific mode All diagnostic messages with SAE J1850 use Cyclic Redundancy Check CRC as the error detection byte ERR Diagnostic messages using the ISO9141 2 standard include a checksum after the data bytes instead of the CRC with SAE J1850 13 The in frame response byte is required in all requests and response messages at 4 6 Kbps but is not allowed for messages at 10 4 Kbps there is no provision for in ae n a frame response This program implements the messages at 10 4kbps so the in frame response is not considered 6 3 Response Message The module in the vehicle responds with the data stored or its status when information is requested by the test equipment The Physical layer interprets this information into frame 14 Figure 6 1 shows the basic flow chart for the data transfer from Physical layer to the Application layer The data obtained from the Physical layer has the same format as shown in Figure 4 1 depending on which protocol is supported by the vehicle The first step in data transfer is to check for errors The error check is performed with the help of a Cyclic Redundancy Check CRC s prescribed by 71850 protocol The CRC byte is obtained from the algorithm described in Chapter 4 In
83. y of Automotive Engineers SAE The SAE has also developed specifications for a low cost hand held diagnostic scan tool that will be capable of communicating with all vehicle makes and models equipped with OBD II systems Consequently service centers will be able to access on board diagnostic information without having to buy a separate piece of diagnostic equipment for every make of vehicle they service 5 2 2 California Code of Regulations CCR California is a pioneer in setting up automobile emission standards The California Code of Regulations CCR includes an enhanced inspection and maintenance I amp M program commonly referred to as smog check II to be implemented with 1996 calendar year This program includes the On Board Diagnostic OBD II system 1 Section 1968 1 of Title 13 California Code of Regulations CCR entitled Malfunction and Diagnostic System Requirements 1994 and Subsequent Model Year Passenger Cars Light Duty Trucks and Medium Duty Vehicles and Engines OBD II was adopted by the Air Resources Board on September 14 1989 The regulation requires manufacturers to implement new comprehensive on board diagnostic systems replacing the original on board diagnostic requirements OBD I found in Title 13 CCR Section 1968 beginning with the 1994 model year 5 10 The on board diagnostic system requires monitoring of engine misfire catalysts oxygen sensors evaporative systems exhaust gas recirculati
84. yte 3 for 1 3 1 lt 6 14 req 1 0X00 else the request for emission related powertrain diagnostic trouble codes if test_mode 0X03 data_byte 1 for 1 1 1 lt 6 1 req 1 0X00 else the request message is to clear or reset emission related diagnostic information if test mode 0X04 data byte 1 for 1 1 1 lt 6 1 req 1 0X00 j else request for oxygen sensor monitoring results if test mode 0X05 data byte 3 for 1 3 1 lt 6 1 req 1 0X00 else 82 request for On Board monitoring Test Results for non continuously monitored system if test_mode 0X06 data_byte 2 for 1 2 1 lt 6 1 req i 0X00 else request for On board monitoring test results for continuously monitored system if test mode 0X07 data byte 7 if pronumber 1 dataframe 0 0x68 dataframe 1 0x6A dataframe 2 OxF 1 else dataframe 0 0x61 dataframe 1 0x6A dataframe 2 0xF 1 j for i 0 i lt 6 i dataframe 3 1 req 1 crc_byte new_crc frame dataframe 10 crc_byte 83 dataframe 11 0x00 Physical dataframe void Physical unsigned char frame int loop for loop 0 loop lt 1 1 sloop printf x frame loop 84 This program is written to detect any error in the frame during the transmission This program implements the cyclic redundancy check to detect errors and is ca

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