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Subaru On-Board Diagnostic Systems

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1. Subaru On Board Diagnostic Systems arly OBD on board diagnostic systems now referred to as OBD I could turn on a malfunction indicator light MIL and store hard fault codes when an emission related system or component fault was detected A hard fault is defined as a fault that is present while the vehicle computer is monitoring a particular circuit or device meaning the fault is not intermittent If the fault went away the MIL was turned OFF by the computer Introduction The Environmental Protection Agency EPA now has regulations in place that establish requirements for on board diagnostic OBD II systems on light duty vehicles and light duty trucks The purpose of the OBD II system is to ensure proper emission control system operation for the vehicle s lifetime by monitoring emission related components and systems for deterioration and malfunction There s a big difference between detecting only hard faults OBD I and having the ability to actively monitor the system for proper operation deterioration or a malfunction OBD II Engines in today s vehicles are largely electronically controlled Sensors and actuators sense the operation of specific components e g the oxygen sensor and actuate others e g the fuel injectors to maintain optimal engine control An on board computer known as the powertrain control module controls all of these systems With proper software the on board computer is ca
2. connectors when you re done A Figure 19 M onitoring A C Relay Operation Subaru On Board Diagnostic Systems New Select Monitor Current Engine Data Display Normal Mode Contents Display Unit of Measure Battery Voltage Battery Voltage V Vehicle Speed Signal Vehicle Speed km h or MPH Engine Speed Signal Engine Speed RPM Engine Coolant Temperature Sensor Signal Coolant Temperature C or F Ignition Timing Signal Ignition Timing degrees Mass Air Flow Signal Mass Air Flow g s or lb m Mass Air Flow Signal Air Flow Sensor Voltage V Throttle Position Signal Throttle Opening Angle o Throttle Position Signal Throttle Sensor Voltage V Injection Pulse Width Fuel Injection 1 Pulse ms Idle Air Control Signal ISC Valve Duty Ratio o Engine Load Data Engine Load o Front Oxygen Sensor Output Signal Front O2 Sensor V Rear Oxygen Sensor Output Signal Rear O2 Sensor V Short Term Fuel Trim A F Correction 1 Yo Knock Sensor Signal Knocking Correction degrees Atmospheric Absolute Pressure Signal Atmospheric Pressure mmHg kPa InHg Intake Manifold Absolute Pressure Signal Manifold Relative Pressure mmHg kPa InHg A F Correction short term fuel trim By Rear O2 Sensor _ Rear O A F Learning Long Term Fuel Trim Whole A F Learning Yo Long Term Whole Fuel Trim Front O A F Learning Yo Front Oxygen Sensor Heater Current Front O Heater A Rear Oxygen Sensor Heater Current Rear O Heater A Canister Purge Control Solenoid Valve Duty R
3. an OBD II compliant Subaru using a generic scan tool e Automatic determination of the communications protocol e Display of the Readiness Test status e Display of the vehicle s Current Data parameters e Display of Freeze Frame Data saved by the control unit e Display of Diagnostic Trouble Codes DTCs saved by the control unit e Clearing Emission Related Diagnostic Information DTCs and diagnostic parameters e Display of O Sensor Test Results e Display of the On Board Monitoring Test Results for Non Continuously Monitored Systems e Display of the On Board Monitoring Test Results for Continuously Monitored Systems We tried out three generic OBD II scan tools on a 1995 Subaru Legacy wagon Although OBD II compliance was not required by EPA regulations until the 1996 model year Legacy models began receiving OBD II equipment during the 1995 model year The 1995 Legacy wagon we used for our testing was fully OBD II compliant The three generic OBD II scan tools we tried out were the OTC Monitor 4000 Enhanced the Vetronix Mastertech and the Snap on Scanner All three scanners successfully interfaced and retrieved information from our Subaru wagon but each took a slightly different method to get there All three scanners have the ability to save information print it or store it to a PC We ll use a series of photos and short captions Poue 4 to show you what we found Figure 1 Aftermarket scanner software typicall
4. atio CPC Valve Duty Ratio o Fuel Tank Pressure Signal Fuel Tank Pressure mmHg kPa InHg Fuel Temperature Signal Fuel Temperature One Fuel Level Signal Fuel Level V Ignition Switch Signal Ignition Switch ON or OFF Automatic Transmission Vehicle Identification Signal AT Vehicle ID Signal ON or OFF Test Mode Connector Signal Test Mode Signal ON or OFF Neutral Position Switch Signal Neutral Position Switch ON or OFF Air Conditioning Switch Signal A C Switch ON or OFF Air Conditioning Relay Signal A C Relay ON or OFF Radiator Main Fan Relay Signal Radiator Fan Relay 1 ON or OFF Fuel Pump Relay Signal Fuel Pump Relay ON or OFF Knocking Signal Knocking Signal ON or OFF Radiator Sub Fan Relay Signal Radiator Fan Relay 2 ON or OFF Engine Torque Control Signal Torque Control Signal ON or OFF Pressure Sources Switching Solenoid Valve Pressure Sources Change ON or OFF Front Oxygen Sensor Rich Signal Front O Rich Signal ON or OFF Rear Oxygen Sensor Rich Signal Rear O Rich Signal ON or OFF Federal Specification Vehicle Identification Signal FED Spec Vehicle Signal ON or OFF Exhaust Gas Recirculation System Diagnosis Signal EGR System Diagnosis ON or OFF Catalyst Diagnosis Signal Catalyst Diagnosis ON or OFF Pressure Control Solenoid Valve PCV Solenoid Valve ON or OFF Exhaust Gas Recirculation Solenoid Valve EGR Solenoid Valve ON or OFF Vent Control Solenoid Valve Vent Solenoid Valve ON or OFF Subaru On Board Diagnostic Systems New Select Monito
5. ble to display the results of the OBD II Readiness Tests All Readiness Tests for Continuous and Non Continuos Monitors are displayed on the same screen Our 1995 Legacy is not equipped with all of the possible OBD II monitors so the Mastertech showed N A for these Figure 6 Figure 7 If the OBD II system has stored a DTC snapshot data will also be stored in the PCM memory The Mastertech has its own snapshot capability that is similar to the PCM s function In Snapshot mode the Mastertech can capture a sequence of data parame ters that you define Road testing the vehicle in this mode may allow you to capture an intermittent fault Fi gure 8 Figure 7 The Snap on Scanner relies on a pair of data cartridges a primary data cartridge and a Fast Track Troubleshooter car tridge that contains additional OBD II diagnostic informa tion These cartridges will take you through 1997 model year import vehicles Figure 8 Figure 9 Because the Scanner handles OBD I and OBD II vehicles a series of qualifying ques tions are required to let the Scanner know which vehicle it s hooked up to The scan ner relies on VIN information to zero in on the specific Subaru model If you want to bypass this routine it s possible to take the OBD Generic menu option Figure 10 pane The Snap on Scanner requires the use of a key in its OBD II diagnostic connector to fine tune the Scanner to the vehicle that is bei
6. cribed number of vehicle trips the PCM will eventually strike the temporary DTC from its memory Until the PCM s set of code removal requirements is met any stored temporary DTC can be viewed under the Temporary Codes Inspection mode on the NSM This mode can be very useful when diagnosing intermittent problems that refuse to reveal themselves during normal troubleshooting activities System Operation Check Mode The last NSM function we re going to look at is the System Operation Check Mode Figure 16 Connecting the two green underdash Check connectors Figure 17 places the vehicle in Check Mode When the ignition is turned ON the CHECK ENGINE light on the Combination Meter will begin flashing OFF and ON and sever al fuel system and emission components will begin cycling OFF and ON This mode can be useful for checking the operation of specific components Using the NSM and the underdash Check connectors it s possible to test one component at a time We selected the A C Compressor Relay Figure 18 then took the NSM under the hood to listen for the compressor clutch to cycle OFF and ON Figure 19 Selecting one component at a time allows you to more closely If the component cycles OFF and ON as it should you can be certain that the wiring between the com ponent and the PCM are okay Running through each system operation check doesn t take long and eliminates a lot of guesswork Don t forget to disconnect the Check
7. ed Figure 9 This feature may also be reduced to One Data Display With Detail Figure 10 Data may also be presented in a graphical format by switching over to the Four Channel Graph or Two Channel Graph screens This converts the NSM into a graphing multimeter Figure 11 The voltage scale of individual inputs can be Figure 8 Six Data amp LED Display adjusted in this mode The graphing function can be especially useful if you re looking for a glitch in a signal If the glitch should occur the display can be held and the results saved to the NSM s memory OBD Menu The NSM also offers full OBD II diagnostic capabilities A menu of the unit s OBD II functions is shown in Figure 12 A complete list of the Current Data Display parameters that are monitored by the NSM for a 1998 Legacy in OBD II mode can be found on page XX This list is shown for illustrative purposes as other Figure 9 Subaru vehicles may have more parameters and some may have less For a com Four Data Display With Max amp Min plete listing of the OBD II parameters for the particular Subaru vehicle you are servicing refer to the appropriate Subaru service manual The NSM allows you to look at up to 12 data parameters at once the same as in the Normal mode Figure 13 Because there will always be more than 12 data parameters you ll need to scroll through the list if you want to see them all in this mode If a particular parameter is not found on the vehicle being test
8. ed the NSM will list no support Figure 7 12 Data Display Figure 10 One Data Display With Detail Freeze Frame Data Display One of the most useful features of OBD II for diagnostic purposes is Freeze Frame Data If the vehicle s OBD II system detects a fault that might cause increased vehicle emissions or might damage the catalytic converter it stores freeze frame data at the moment the fault occurred So instead of being left with just a Diagnostic Trouble Code DTC to work with we also have freeze frame data to help Figure 12 0BD Menu us with our diagnosis 74K nE es Diagnostic Trouble Codes DTC Display OBD II regulations require the use of standardized DTCs There s no longer a need to learn the diagnostic language of individual vehicle manufacturers Diagnostic Trouble Code DTC definitions and numbers were prescribed by the Society of Automotive Engineers SAE under J2012 Powertrain DTCs beginning with the prefix P0 have standardized meanings and may be used by all vehicle manufacturers Powertrain DTCs beginning with the prefix P1 are considered manufacturer specific and may be used to define sys tems or functions that are unique to a particular manufacturer or a vehicle from that manufacturer While this system of identification eliminates most of the confusion surrounding DTC definitions it also multiplies the number of available DTCs for a particular vehicle by seve
9. ehicle Figure 5 ic System EGI EM PI Diagnosis The EGI EMPI Diagnosis menu allows the choices shown in Figure 6 The Current Data Display amp Store option allows the user to monitor a wide range of engine management system inputs and outputs using the vehicle s serial data interface and the OBD II connector A listing of the information available in this mode is shown on page 10 A maximum of 12 different inputs can be displayed on the NSM screen at once 12 Data Display so it will be necessary to scroll up or down through the data if you want to see everything that s being monitored by the NSM Figure 7 Most diagnostics will not require you to see all of the data at once so it s best to limit your choices to related information only This speeds up the unit s refresh rate cuts the clutter on the LCD and makes it easier for you to monitor data from particular inputs In addition to 12 Data Display there are several other ways to look at the data Six Data amp LED Display Figure 8 allows you to chose up to six different data inputs then display them in numerical form The status of four ON OFF inputs are also displayed along the right side of screen Red LEDs turn ON or OFF to indicate the status of these inputs This function is similar to the original Select Monitor If you re looking for an input that may be going out of range or want to track something over time the Four Data Display With Max amp Min may be select
10. k 1 ON or OFF Engine Load o Coolant Temperature C or F Short Term Fuel Trim B1 H Long Term Fuel Trim B1 o Manifold Absolute Pressure mmHg kPa InHg Engine Speed RPM Vehicle Speed km h or MPH Ignition Timing Advance 1 Mass Air Flow g s or lb m Throttle Opening Angle o Oxygen Sensor 11 V Short Term Fuel Trim 11 Oxygen Sensor 12 V Short Term Fuel Trim 12 OBD System Freeze Frame Data OBD M ode Diagnostic Trouble Code DTC For Freeze Frame Data Air Fuel Ratio Control System For Bank 1 Engine Load Data Engine Coolant Temperature Signal Short Term Fuel Trim By Front Oxygen Sensor Long Term Fuel Trim By Front Oxygen Sensor Intake Manifold Absolute Pressure Signal Engine Speed Signal Vehicle Speed Signal Freeze Frame Data PIC Fuel System For Bank 1 ON or OFF Engine Load o Coolant Temperature Cor F Short Term Fuel Trim B1 Yo Long Term Fuel Trim B1 o Manifold Absolute Pressure mmHg kPa InHg Engine Speed RPM Vehicle Speed km h or MPH Oxygen Sensor Monitoring Test Results Oxygen Sensor For Monitoring Test Rich To Lean Oxygen Sensor Threshold Voltage Lean To Rich Oxygen Sensor Threshold Voltage Low Oxygen Sensor Voltage For Switch Time Calculation High Oxygen Sensor Voltage For Switch Time Calculation Rich To Lean Oxygen Sensor Switch Time Lean To Rich Oxygen Sensor Switch Time Maximum Oxygen Sensor Voltage For Test Cycle Minimum Oxygen Sensor Voltage For Test Cycle lt Q Se
11. ng tested Figure 10 Figure 11 OBD II Current Data parameters are displayed six at a time across the Scanner s LCD Scrolling with the unit s thumbwheel takes you through all parameters i All other generic OBD II scanner functions are also supported by the Snap on Scanner Figure 11
12. nsor Monitor gt Rich To Lean Sensor Volt Lean To Rich Sensor Volt Low Sensor Voltage lt lt lt lt High Sensor Voltage Rich To Lean Switch Time sec Lean To Rich Switch Time sec Maximum Sensor Voltage V Minimum Sensor Voltage V SUBARU Generic Scan Tools One of the biggest advances that OBD II brought to vehicle repair was the ability of a generic scan tool to communicate with any OBD II compliant vehicle OBD II regulations spell out a specific way that all vehicles must communicate with these generic scan tools It s no longer necessary to have a drawer full of adapters and testers to communicate with the various vehicles your shop may happen to work on Since all 1996 and later Subaru vehicles must comply with OBD II regulations we decided to try out an assortment of generic scan tools on an OBD II compliant 1995 Subaru Legacy The Legacy came on line with OBD II capability during the 1995 model year while the Impreza made the 1996 deadline All Forester and Outback models are also OBD II compliant None of the generic scan tools we tested offer the versatility and wealth of data found in the New Select Monitor Unless you plan on doing an awful lot of Subaru OBD II repairs you may not be able to justify the expense of a New Select Monitor purchase If you already own or plan to purchase a generic scan tool with OBD II updates at the very least you will be able to retrieve the following information from
13. pable of monitoring all of the sensors and actuators to determine whether they are working as intended It can detect a malfunction or deterioration of the various sensors and actuators usually well before the driver becomes aware of the problem through a loss in vehicle per formance or driveability The sensors and actuators along with the diagnostic soft ware in the on board computer make up what is called the OBD II system The purpose of the OBD II system is to assure proper emission control system operation for the vehicle s lifetime by monitoring emission related components and systems for deterioration and malfunction There are circumstances under which the vehicle computer will detect a system problem before the driver notices a drive ability problem Furthermore OBD II can detect problems that may not be notice able upon visual inspection because many component failures that have an effect on emissions can be electrical or even chemical in nature By detecting these emis sion related failures and alerting the driver to the need for potential repair vehicles can be properly repaired before emissions become a problem When the OBD II system determines that a problem exists a corresponding Diagnostic Trouble Code DTC is stored in the computer s memory The computer also illuminates a dashboard CHECK ENGINE light This light serves to inform the driver that a problem has been detected and vehicle service is needed When the ca
14. r Current Data OBD Mode Contents Number Of Diagnostic Code Malfunction Indicator Lamp Status Monitoring Test Of Misfire Monitoring Test Of Fuel System Monitoring Test Of Comprehensive Component Test Of Catalyst Test Of Heated Catalyst Test Of Evaporative Emission Purge Control System Evaporative Purge System ON or OFF Test Of Secondary Air System Test Of Air Conditioning System Refrigerant Test Of Oxygen Sensor Test Of Oxygen Sensor Heater Test Of Exhaust Gas Recirculation System Air Fuel Ratio Control System For Bank 1 Engine Load Data Engine Coolant Temperature Signal Short Term Fuel Trim By Front Oxygen Sensor Long Term Fuel Trim By Front Oxygen Sensor Intake Manifold Absolute Pressure Signal Engine Speed Signal Vehicle Speed Signal Ignition Timing Advance For 1 Cylinder Mass Air Flow Signal Throttle Position Signal Front Oxygen Sensor Output Signal Air Fuel Ratio Correction By Front Oxygen Sensor Rear Oxygen Sensor Output Signal Air Fuel Ratio Correction For Rear Oxygen Sensor On board Diagnostic System Display Unit of Measure Number Of Diagnostic Code MIL Status ON or OFF Misfire Monitoring ON or OFF Fuel System Monitoring ON or OFF Component Monitoring ON or OFF Catalyst Diagnosis ON or OFF Heated Catalyst ON or OFF Secondary Air System ON or OFF A C System Refrigerant ON or OFF Oxygen Sensor ON or OFF Oxygen Sensor Heater ON or OFF EGR System Diagnosis ON or OFF Fuel System For Ban
15. r is delivered to the repair shop a service technician can quickly retrieve the stored diagnostic trouble codes from the computer memory of the vehicle using newly developed diagnostic tools Since the diagnostic trouble codes will specifical ly identify the problem the service technician can more quickly and accurately make the proper repair The following is a brief description of the Subaru OBD II system e The Subaru on board diagnostic OBD II system has the ability to detect and indicate faults in various inputs and outputs of the vehicle s electronic control systems A CHECK ENGINE malfunction indicator lamp MIL in the combin tion meter indicates the occurrence of a fault or trouble A fail safe function is provided to ensure minimal driveability in the event of a failure of a component or sensor that may disable the electronic control system The OBD II system incorporated in all Subaru vehicles since 1996 complies with Section 1968 1 of the California Code of Regulations OBD II regulation and all applicable Federal Clean Air Act regulations The OBD II system monitors co ponents and system malfunctions which may have an effect on emissions When the system decides that a malfunction has occurred the MIL illuminates At the same time that the MIL illuminates or blinks a diagnostic trouble code DTC and freeze frame data of engine conditions are stored in the on board computer s memory When it detects a malfunction the OBD II
16. ral fold We checked the powertrain DTC list for a late model Subaru Legacy and found there were over 100 possibilities There s no way you re going to Figure 14 Stored DTC Display be able to memorize all those DTCs so reliable service information becomes even more important than it has been in the past We intentionally triggered several DTCs to produce the list of DTCs shown in Figure 14 DTCs can also be cleared using the NSM but be advised that the freeze frame data that goes along with the DTCs will be erased at the same time Other OBD Mode Features The NSM can also access the PCM to monitor O sensor operation 02 Sensor Monitor Test Information obtained during this test includes rich to lean and lean to rich threshold voltages and times and low high sensor voltages for switch time calculations Figure 15 This data can be especially useful if a lazy or dying oxygen sensor is suspected The numbers shown here don t lie Some DTCs are considered to be temporary meaning they haven t yet met the criteria to trigger the Malfunction Indicator Light MIL Perhaps a fault was detected just once then not repeated While this may not be enough to trigger the MIL it doesn t mean the PCM s OBD II function looks the other way Quite the contrary Figure 16 The PCM will store this information under a temporary DTC If the conditions that System Operation Check Mode triggered the original temporary DTC are not repeated for a pres
17. s to function as an OBD II diagnostic interface with Subaru vehicles Since OBD II standards and protocols are common to all OBD II compliant vehicles the NSM could also be used for OBD II diagnosis on other vehicles With the substitution of a domestic or generic OBD II data cartridge the NSM could have the capability to function with vehicles built by manufacturers other than Subaru The hand held NSM display screen measures 95 mm by 71 mm and provides a backlit LCD screen with adjustable contrast Twelve functions can be displayed on the screen at the same time and ON OFF signals can be monitored by observing illuminated LEDs at the side of the LCD screen This function is similar to the origi nal Select Monitor diagnostic tools Figure 1 which the NSM is designed to replace Four channels of graphical information can be displayed at the same with the ability to adjust values per division and time base A memory feature is built in powered by four AA batteries that maintain memory when the NSM is turned off Memory capacity is 256K bytes Information stored on the NSM can be outputted to a printer using an infrared or conventional printer interface Software to download stored NSM diagnostic information to a PC will also be offered by Hitachi The NSM has many features several of which we will describe with the following text and photographs We re concentrating primarily on OBD II and engine manage ment diagnosis in this iss
18. system stores freeze frame engine condition data engine load engine coolant temperature fuel trim engine speed and vehicle speed etc into the on board computer memory If the OBD II system detects various malfunctions including a fuel trim fault or misfire the OBD II system first stores freeze frame engine conditions about the fuel trim or misfire If the malfunction does not occur again for three trips the MIL turns off but the DTC remains in the on board computer s memory The OBD II system is capable of communication with a generic scan tool OBD II generic scan tool defined by ISO 9141 CARB specifications The OBD II diagnostic procedure is different from the usual diagnostic proc dure When troubleshooting Subaru OBD II vehicles it is necessary to connect a Subaru Select Monitor or New Select Monitor to the vehicle If these tools are not available a generic OBD II scan tool may also be used SUBARU Subaru On Board Diagnostic Systems Figure 1 Original Select M onitor New Select Monitor The Hitachi Auto Systems Company Ltd is the manufacturer of the Subaru New Select Monitor NSM While this tool was originally supplied to Subaru deal ership technicians Hitachi has announced that it also plans to offer it to the automo tive aftermarket at some time in the future At present information on specific Subaru models is provided on interchangeable data cartridges One of the NSM s main capabilities i
19. ue of The End Wrench so after the next three photos we ll be connected to a 1997 Subaru Outback equipped with a 2 5 liter engine The additional capabilities of the NSM for diagnosis of other Subaru vehicle systems as well as its multimeter and scope capabilities will be discussed in future issues of The End Wrench NSM Main Menu After inserting the proper data cartridge and turning on the NSM the Main Menu comes into view Figure 2 The NSM has the capability of monitoring and diagnosing several Subaru vehicle systems using the OBD II diagnostic connector Figure 3 Earlier pre OBD II Subaru vehicles can also be accessed by the NSM using the proper adapter cable and the vehicle s conventional underdash diagnostic connector Figure 4 The NSM can also serve as a digital multimeter a two channel scope meter actually a graphing multimeter and it can save data to its internal memory The 1993 Legacy we initially connected the NSM to gave us the possibility of access to the following vehicle systems e EGI EMPI fuel system e AT ECTV automatic transmission or electronic continuously variable transmission e Air Conditioning System e Cruise Control e ABS TCS e 4WS e Air Suspension System The NSM lists all of the possibilities for a particular model year range then attempts to communicate with all of the systems that are present on the subject vehicle All of the systems listed here probably won t be present on a single v
20. y lags a year or two behind the current vehicle model year This Import 96 cartridge is the most recent data cartridge available for the OTC Monitor 4000 Enhanced Figure 2 The Monitor asks you a series of qualifying questions to identify the vehicle These Figure 2 questions are necessary because the data cartridge contains information on both OBD I and OBD II vehicles An OBD II only cartridge wouldn t need to know what type of vehicle you were working on because the data exchange protocols are standardized and the diagnostic link connector DLC is always the same Figure 3 When we got through with the qualifying questions we found that the Monitor had OBD information on the Engine PCM as well as the ABS and Airbag systems The ABS and Airbag information dealt primarily with DTC retrieval Figure 3 Subaru On Board Diagnostic Systems Figure 4 The Vetronix Mastertech offers a generic OBD II car tridge This means that it s unnecessary to answer any qualifying questions Just plug the unit s diagnostic con nector into the DLC and you re ready to go After com municating with the vehicle s PCM the Mastertech tells you what OBD II options are available for the vehicle Figure 4 Figure 5 The Mastertech s large LCD allows you to simultaneously view up to 12 different current data points Scrolling up or down allows you to see all of the available data Figure 6 Figure 5 ll generic scan tools must be a

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