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1. 3 NOBLE or PRECIOUS METALS LOADING These materials commonly Platinum Palladium and Rhodium are the elements that make the catalytic reaction to reduce pollutants The definition of the word catalyst means that something causes a reaction without itself being consumed or changed in that reaction The metals can be used to gether or by themselves It should be noted that OEM OBD II catalysts contain an aver age of about twice the precious metal loading of their non OBD II counterparts Now that you know what comprises a catalytic converter you can see a very important difference between OBD Il and Non OBD II catalytic converters OBD II catalytic con verters must have excellent oxygen storage capacity Other chemicals and compounds are added into the washcoat of OBD II converters to aid in this oxygen storage capacity If the oxygen storage capacity is not good the MIL will illuminate Please refer back to the Catalyst Monitor section of this publication WHAT ARE THE PARTS OF AN OBD II SYSTEM AND HOW CAN FIND THEM CRANKSHAFT POSITION SENSOR The purpose of this sensor is to give the engine speed to the vehicles computer so that it can send spark at the appropriate time to the right cylinder a There are three types of CKP s crankshaft position sensors used The first ish the Hall Effect which works by using a slotted wheel and a magnetic field and P this information is sent to the computer The second is the Magnetic P
2. PO460 PO461 PO462 PO463 PO464 PO465 ENGINE RELATED DTCs Exhaust Gas Recirculation Flow Malfunction Exhaust Gas Recirculation Flow Insufficient Exhaust Gas Recirculation Flow Excessive Exhaust Gas Recirculation Circuit Malfunction Exhaust Gas Recirculation Circuit Range Performance Exhaust Gas Recirculation Sensor A Circuit Low Exhaust Gas Recirculation Sensor A Circuit High Exhaust Gas Recirculation Sensor B Circuit Low Exhaust Gas Recirculation Sensor B Circuit High Secondary Air Injection System Malfunction Secondary Air Injection System Incorrect Flow Secondary Air Injection System Switching Valve A Circuit Malfunction secondary Air Injection System Switching Valve A Circuit Open secondary Air Injection System Switching Valve A Circuit Shorted Secondary Air Injection System Switching Valve B Circuit Malfunction Secondary Air Injection System Switching Valve B Circuit Open secondary Air Injection System Switching Valve B Circuit Shorted Catalyst System Efficiency Below Threshold Bank 1 Warm Up Catalyst Efficiency Below Threshold Bank 1 Main Catalyst Efficiency Below Threshold Bank 1 Heated Catalyst Efficiency Below Threshold Bank 1 Heated Catalyst Temperature Below Threshold Bank 1 Catalyst System Efficiency Below Threshold Bank 2 Warm Up Catalyst Efficiency Below Threshold Bank 2 Main Catalyst Efficiency Below Threshold Bank 2 Heated Catalyst Efficiency Below Threshold Bank 2 Heated Catalyst Tempe
3. is greater than 0 3 and oxygen O2 is greater than 0 4 the converter is most likely defective You remove a defective converter from a car and it has melted down What could have caused the converter to melt down A step by step approach is needed to find the answer so let s start at the begining TESTING OF CONVERTERS FUEL Unleaded fuel must be used in vehicles with a catalytic converter Using leaded fuel will cause the converter to become plugged and inoperative Also some gas additives can damage a converter Always check the instruction label of any additive added to your fuel system to be sure that it is converter safe OXYGEN SENSOR This sensor sends information to the ECU Electronic Control Unit to maintain proper air fuel mixture It is located either in the exhaust manifold pipe or catalytic converter As an oxygen sensor operates it checks to see if oxygen is present in the system If no oxygen is detected this would indicate a rich mixture and the oxygen sensor will read about 900mV millivolts when excessive amounts of oxygen are present the sensor voltage will read about 100mV Rich mixtures mean high readings lean mixtures mean low readings Please note taht the exhaust temperature must be at least 600 degrees Farenheit for the sensor to operate The measurements should only be taken with a multimeter that has a 10 meg ohm impedance rating Failure to follow this rule may cause you to replace the vehicles E
4. CO carbon monoxide pass through the substrate they are converted into less harmful compounds such as CO carbon dioxide H O water and N nitrogen This conversion starts at temperatures around 250 Celsius RULES REGARDING THE DEVELOPMENT OF AFTERMARKET CATALYTIC CONVERTERS Rules for the development of converters that satisfy EPA requirements are set forth in the Federal Register Briefly the rules state that the converter manufacturer must submit two catalyst samples to an independent laboratory who will accumulate 25 000 miles or its equivalent on each of the catalysts The catalysts are then tested for emissions performance and must convert a minimum of 70 Hydrocarbons and Carbon Monoxide and 30 NOX on a worst case vehicle A worst case vehicle is defined as having the largest engine displacement and heaviest test vehicle weight that the converter manufacturer intends to cover with the catalyst Currently the United States EPA requires the aftermarket converter manufacturer to warranty that the converter will not cause the MII check engine light to illuminate within the 25 000 mile required warranty period of the substrate that has met all the prior EPA requirements Section Two THE BASICS OF VEHICLE EMISSION SYSTEM_ TROUBLESHOOTING A customer walks into your shop his car is stalling and will not run above 20 mph You check the car out and tell him the catalytic converter is bad and you replace it Off he goes
5. measure the resistance across the sensor then reconnect the sensor harness and run the engine for 3 to 5 minutes until it reaches normal operating temperature Disconnect the wire harness and again measure resistance across sensor Ifthe difference between cold and hot readings is less than 200 ohms the sensor is defective POSSIBLE EXHAUST EMISSION DEVICE PROBLEMS AND CAUSES BLACK EXHUAST SMOKE Oxygen Sensor Coolant Temp Sensor Map Sensor Air Change Sensor STRONG EXHAUST SMELLS Catalytic Converter Map Sensor Air Change Sensor MELTED CONVERTER Oxygen Sensor Fuel System Problems Ignition Problems Map Sensor Vehicle Overload CONVERTER PROBLEM FLOW CHART VENICE PAILS PLUGGED OR MELTDOWN DAMAGE TO CONVERTER GETS CONTAMINATED SHELL OR PIPE EMISSION TEST RED HOT CONVERTER CHECK SPARK CHECK FUEL TYPE PLUGS WIRES amp USED IGNITION SYSTEM SEE CHART C CHECK IF ANY ADDITIVES WERE USED CHECK TIMING amp IDLE ADJUSTMENTS CHECK FOR EXCESSIVE OIL BURNING CHECK AIR FUEL ADJUSTMENTS CHECK FOR RTV SILICONE CONTAMINATION OR HC READING HIGH ANTIFREEZE LEAK INTO SEE CHART B COMBUSTION CHAMBER CO READING HIGH SEE CHART A REPAIR CAUSE OF OVERHEATING CONVERTER REPLACE CONVERTER CHART A CHART B CHART C POSSIBLE HIGH CO READING POSSIBLE HIGH HC FAULTY IGNITION CAUSES READING CAUSES COMPONENTS THAT l CAN DAMAGE A Improper
6. sensor is bad this too can lead to converter damage If the injection system uses a cold start injector which is a small injector used to richen the mixture by injecting fuel into the intake air stream when the engine is cold better the converter efficiency The catalytic washcoat also stores excess oxygen from lean operating cycles and releases it for use during rich cycles If this injector is leaking or dripping or if its temperature sensor is not operating properly this too can damage the converter Because of the many different injection systems used consult the proper manual when diagnosing this system the Fuel Injection System is monitored by the Fuel Monitor another continuous monitor MASS AIR FLOW SENSOR This sensor measures the volume of intake air It is tested with a special tester or a computer scan tool If it is defective it can cause problems from rough idles eo to no start and poor fuel economy Most of the previously talked about systems and devices can be tested with the use of a scan tool There are many types of this tool so please consult tool maker s informa tion for proper hookup While some of these tools are expensive they are well worth the cost when you realize how useful they are For the OBD II system you should consider the CATCO T9035 its help to you will certainly outweigh its cost MAP SENSOR This sensor tells the ECU how much air is entering the engine as well as the load on the en
7. their direct fits so that any isulation is included with the direct fit assembly IGNITION SYSTEM Many parts are used in the ignition system This system delivers the voltage or spark to the appropriate cylinder to fire the engine Any of the following problems can cause the converter to fail or be damaged fouled spark plugs bad spark plug wires or carbon tracked distributor cap Make sure all spark plugs and wires are firing properly A misfiring plug not only wastes gas but it makes the mixture rich and in time will ruin the converter Be sure to check distributor timing and vacuum advance for proper operation Some cars also use a system called Distributerless or Coil Pack where the ignition coil is connected right to the spark plug and the coil is fired through the computer FUEL INJECTION SYSTEM Problems in the fuel injection system can also cause problems with the a converter Fuel injection systems differ greatly Basically a fuel injection MARA system uses small electrically controlled solenoids that deliver or inject fuel __ into the throttle body or into the intake part of the engine These little 2 solenoids are controlled by a computer which obtains information from various sensors located throughout the engine This sensor helps the computer determine how much fuel to inject If an injector is leaking internally or dribbling fuel into the engine it may damage the converter Ifthe oxygen sensor is defective or the map
8. washcoated substrate These metals are what serve to cause the catalytic reaction The definition of a catalyst is a material which increases the rate of a chemical reaction while it is treated during the noble metal and washcoat process it passes through an oven process which removes excess water and calcines in the substrate This means it removes all traces of the chemical carriers which are used to deposit the noble metals during the preparation of the catalyst 4 SHELL This is the stainless steel enclosure which the substrate is contained In 5 INNERAM This is a ceramic fiber based material which is wrapped around the ceramic substrate It acts as a vibration cushion as a seal to prevent exhaust gas from by passing the substrate and as an insulator to keep the heat from the substrate from transferring into the shell Some types of inneram can also be made of stainless wire or silica materials Generally as a rule metallic type substrates do not use inneram 6 HEAT SHIELD This is used to prevent the heat of the catalyst from causing any damage or fires to the under body or components of the vehicle 7 END PIPES The stainless steel tubes used to connect the catalytic converter to the vehicles exhaust system HOW DOES THE CONVERTER WORK As the exhaust flows through the substrate inside the converter housing the catalytic reaction takes place As the pollutants like NO nitrogen oxide HC hydro carbon and
9. 00 rom When checking exhaust back pressure be sure to check at the inlet and outlet of each converter or exhaust component tested A reading of 1 2 to 2 psi is normal By using a plug with the same thread as an oxygen sensor you can remove the O2 sensor install the plug into the hole and connect it to your back pressure gauge To do this you will need to obtain a plug with an 18mm x 1 25 thread This plug may be purchased at any auto parts store under the name of Spark Plug Non Fouler Adapter You can also save one out of a CATCO catalytic converter that comes with one You will then need to fix a small piece of 1 8 O D tube to the back side of the plug This will serve as a way to connect it to your gauge by the vacuum hose If additional help is needed call the CATCO technical hotline at 800 247 2515 EXHAUST GAS ANALYZER TEST A gas analyzer will tell you if the converter is functioning properly By checking your CO carbon monoxide reading you will be able to tell if the system is operating rich Hooking up the machine differs according to the model and brand of analyzer being used Consult the analyzer manual for instructions Once you have determined that the converter has failed the next step should be to find out why it failed As a rule of thumb the following will usually be correct over 95 of the time if the tail pipe reading shows that hydrocarbons HC are higher than 125 ppm but less than 400 ppm and carbon monoxide CO
10. CATCO CATALYTIC CONVERTERS gt Worldwide Source for Technologically Advanced Catalytic Converters na ai DRS a SOLUTIONS 2 A Catalytic Converter Information Booklet And A Diagnostic Manual r For Troubleshooting Catalytic Converter Problems Replacement And Questions t gg 2010 Airtek Inc Contents section One Catalytic Converter general information section Two General guidelines non OBD ll systems Section Three OBD OBD II systems section Four IM 240 or equivalent testing section Five EPA rules regulations Section One CATALYTIC CONVERTERS A catalytic converter is a device that chemically changes the harmful components of Internal Combustion engine exhaust into harmless gasses A converter is made up of several parts 1 SUBSTRATE serves as the internal structure to which the catalyst washcoat and noble metals are deposited upon It is through this substrate that the engine exhaust flows through or comes in contact with to have a chemical reaction a PELLET TYPE small ceramic pellets are treated with washcoat and noble metals They are held in place inside the converter body in a cage The exhaust gas passes over them There could be a couple of hundred thousand pellets in the average converter The main disadvantage of this converter is the high exhaust back pressure b CERAMIC MONOLITH TYPE Also known as the honeycomb type This ceramic type substrate has th
11. CU A properly functioning sensor will O oscillate between 900mV and 100mV every few seconds You can measure this with your multimeter If the reading does not oscillate or stays fixed the sensor is defective Also note that silicone from either antifreeze or RTV silicone sealant can clog an oxygen sensor and make it defective If the vehicle has a coolant leak into the combustion chamber the sensor should be replaced When using a silicone sealer make sure it is oxygen sensor safe Consult the last pages of this catalog for wiring information on O2 sensors Also note there are two types of oxygen sensors The Zirconia the most common type works by generating a voltage The Titania type works by varying its resistance IGNITHON SYSTEM Many parts are used in the ignition system This system delivers the voltage or spark to the appropriate cylinder to fire the engine Any of the following problems can cause the converter to fail or be damaged fouled spark plugs bad spark plug wires or carbon tracked distributor cap Make sure all spark plugs and wires are firing properly A misfiring HS plug not only wastes gas but it makes the mixture rich In time this will ruin the converter Be sure to check distributor timing and vacuum advance for proper operation CARBURETOR SYSTEM A carburetor is a device that mixes gasoline with air and delivers it into the intake manifold for the engine to burn If a carburetor is worn or defect
12. ENGINE COMPUTER ECS Engine Control System PCM Powertrain Control Module This is the unit that controls all the functions of the engine powertrain Everything from how much fuel to the when a cylinder fires to max engine speed and timing are controlled by this unit All the signals from the various sensors are sent to this part and all commands back to the various systems come from it There are many other sensors used in modern vehicles such as Detonation Sensors Power Steering Cut Off Sensor Switches Throttle Position Sensors Vehicle Speed Sen sors and sensors used to turn cooling fans on Make sure you have the proper manual for the system you are working on This booklet has only covered the main parts and systems that make the engine operate This booklet is intended to give you background and insight on how the OBD II system works and how to repair it Only the proper repair manual and experience can answer all questions EMISSION TESTING AND OBD II Since most states have gone to some form of enhanced emissions testing ie I M 240 let s discuss the OBD II system and how it relates to the emission test process The I M 240 test is an enhanced procedure that was designed to demonstrate real world driving conditions Prior to this test procedure most states used a Static or Un loaded test where the emissions were sampled out of the tail pipe without the vehicle being under any load The I M 240 procedure
13. This type of wave form is proper for the O2 sensors that are located before the catalytic converter EXAMPLE PP En PATT E R N l The voltage is generated by a sensor that has a probe assembly which contacts the ex haust stream This probe assembly is made up of a compound called zirconium dioxide which is an electrically conductive material that can generate small voltages when in contact with oxygen The probe tip is also coated with platinum to aid in this process The downstream or after converter oxygen sensors measure the amount of oxygen present in the exhaust after the converter Generally the wave form of a system with a properly operating catalyst will show little or no voltage fluctuation on an oscilloscope EXAMPLE PATTERN A ee The catalytic converter is comprised of an internal substrate onto which a chemical washcoat is placed It extends the geometric surface area of the substrate and also acts as an absorbing or storing material for oxygen in the exhaust On to this substrate the precious metals are impregnated that cause the catalytic reactions with the pollutants A Ceramic Monotlith Substrate shown When the engine burns a lean air fuel mixture high amounts of oxygen from the exhaust stream flow through the substrate of the catalytic converter The washcoat on the sub strate absorbs this excess O2 and stores it for use during rich air fuel mixtures when it is released to help in the oxidation proces
14. ad to damage of the air pump diverter valve or the high temperature hose if left unchecked If hoses are melted or components like the air pump or the diverter valve are damaged check the exhaust check valves y Converter Air Tubes These tubes route air into the catalyst to help aid in the oxidation process Check to make sure it is Z A connected and that it is not rusted through S DIVERTER VALVE This valve helps to route air to the exhaust manifold or catalytic converter to assist in maintaining proper emissions Operation should be checked and a manual should be consulted regarding proper cw test procedures EGR SYSTEM This system routes small amounts of exhaust gasses back to the intake manifold to reduce oxides of nitrogen or NOX Systems vary by design so you need to consult the proper manual for the vehicle you are working on Some newer systems also use an EGR valve position sensor If the exhaust system you are working on has one it must be checked also While a bad EGR system will not lead to a converter failure it might be the reason why the vehicle has a NOX problem The EGR valve should be checked according to the vehicle manufacturers procedure to determine if it and its system components are functioning properly Make sure the valve moves m when vacuum pressure or electric signal are applied and that the passages are open and not plugged with carbon Also check any switches relays or solenoids that a
15. al engine problems stuck engine thermostat corroded radiator internally air flow to radiator plugged blocked or corroded cool ing passages carbon deposits system component problems Inoperative EGR valve or system Plugged EGR passages Bad air diverter valve Extremely lean air fuel ratio Bad heat riser valve Malfunctioning radiator fan motor or switch Advanced ignition timing Bad feedback sensor Usually if a converter passes HC and CO but fails NOX the problem is not the convert er Use this rule for determing a non functioning converter It will be accurate 95 of the time or better If the tail pipe reading shows the CO is greater than 0 3 O2 is greater than 0 4 HC ts higher than 125 ppm but not less than 400 ppm the converter is most likely defective Exhaust emission effects due to engine problems Ignition System Malfunction Retard Timing Advance Timing Inoperative Air Injection Faulty EGR Fuel System Rich Fuel System Lean HC Increase Little Change Small Increase Increase Little Change Increase Increase CO Decrease Generally no change Little Change Increase Generally No change Increase Decrease NOX Decrease Decrease Increase No change Increase Decrease Increase Section Five For the most part the rules or guidelines for aftermarket converters are quite clear and concise It is permissable to install an afterma
16. but did you really fix his problem Was the old converter melted down and plugged Why had it failed Will the customer come back with the same problem Did replacing the converter really fix the problem or just remedy it temporarily This booklet will try to help you answer these questions and give you some direction in diagnosing and reparing emission system failures CONVERTERS WHAT DO THEY DO A catalytic converter is a device located in the exhaust system of all cars and most light trucks produced since 1975 It chemically changes pollutants like carbon monoxide hydrocarbons and nitrogen oxide into harmless substances like carbon dioxide nitrogen and water vapor A converter uses an inside structure called a substrate that is plated with precious metals such as platinum palladium and rhodium These elements cause the chemical change TESTING OF CONVERTERS THE THUMP TEST Thump the converter with your fist If it is a monolith type and you hear pieces moving around inside the converter chances are the substrate has come apart If itis a pellet type you should hear pieces moving when you hit it If you do not chances are the pellets have melted together THE VACUUM TEST By using a vacuum gauge you can tell if the converter is plugged Connect the gauge to a manifold vacuum source and quickly move the throttle to midway of its travel then let it snap back to idle A proper vacuum reading will be about 15 20 in Hg at idle When yo
17. defective Note that silicone from either antifreeze or RTV silicone sealant can clog an oxygen sensor and make it defective If the car has a coolant leak into the combustion chamber the sensor should be replaced When using a silicone sealer make sure it is oxygen sensor safe Also note there are two types of oxygen sensors The Zirconia the most common type works by generating a voltage The Titania works by varying its resistance Remember how many things are monitored by the oxygen sensor in the OBD ll system This is the most important part in catalyst monitoring NOTE When using a universal converter in place of a direct fit make sure the post converter O2 sensor is in the same position on the replacement as it was on the original converter Measure the distance from the outlet end of the converter substrate on the Original unit to the O2 sensor port location When installing the new universal converter make sure to install it so that the O2 sensor will be at the same distance in relation to the outlet end of the new substrate as the original unit was Keep in mind that not all oxygen sensors operate the same Consult the catalog on proper replacement sensor applications Removal of insulation or change to the pipe exc insulated pipes can Cause codes pointing to a converter malfunction that is not the fault of the converter If you are using a universal converter please keep this in mind If in doubt use the direct fit Catco engineers
18. e it can also isolate and determine which cylinder misfired This is done through the vehicles computer monitoring sensor signals not only from the crankshaft position sensor but also the camshaft position sensor If a misfire occurs excess hydrocarbons can be released into the exhaust gas which can damage the catalytic converter When the computer detects a misfire it will illuminate the MIL The Misfire Monitor is a Continuous Monitor type It monitors a system constantly and is very important to the OBD II sys tem HOW CAN THE OBD II SYSTEM BE USED TO DIAGNOSE EMISSION PROBLEMS The OBD II vehicle computer can be invaluable in diagnosing what is causing a vehicle to have emission problems and MIL illumination This system was designed with SAE Society of Automotive Engineers guidelines that make the system economical and easy for all technicians to use It uses a data connector or link in which all of the pins or connections are the same no matter who the vehicle manufacturer is This enables a technician to purchase one OBD II reader or scan tool and be able to use this tool on all vehicles Another guideline called for easy access to the location of this data connector The guidelines also called out for a standardized system of fault code identifications This way all vehicle manufacturers would use the same codes to show MIL illuminating DTCs Diagnostic Trouble Codes HOW DO YOU USE THE DATA LINK TO DIAGNOSE PROBLEMS First you wi
19. e is cold and it is leaking or dripping or if its temperature sensor is not operating properly this too can damage the converter Because of the many different injection systems used consult the proper manual when diagnosing this system MASS AIR FLOW SENSOR This sensor measures the volume of intake air It is tested with a special tester or a computer scan tool If it is defective it can cause problems such as rough idles no start and poor fuel economy Most of the previously talked about systems and devices can be tested with the use of a scan tool There are many types of this tool so please consult tool makers information for proper hookup While some of these tools are expensive they are well worth the cost when you realize how useful they are MAP SENSOR This sensor tells the ECU how much air is entering the engine as well as the load on the engine It also monitors barometric pressure When this sensor fails it can cause a rich condition which can damage the converter Because testing of these sensors vary between make and model consult the manual beore testing Generally there are two types the voltage type and the frequency type To check the voltage type you would use a volt meter and a vacuum pump To check the frequency type you would use a tach and a vacuum pump CANISTER PURGE VALVE This vacuum operated valve vents fuel vapors from the carburetor bowl to the charcoal canister If the diaphragm becomes ruptu
20. econds E Decelerate to 35 40mph and run at steady throttle for 1 minute F Drive between 20 45mph for 4 minutes but do not operate under open throttle G Decelerate and idle for 10 seconds H Accelerate to 55mph using no more than 1 2 throttle for 10 seconds Drive 40 55mph using steady throttle for 1 1 2 minutes Shut the vehicle off when you return to the shop If time permits run the cycle again afte the vehicle has cooled off Doing so will ensure that all Flags have been set all problems have been repaired and the vehicle will pass an I M 240 test OTHER OBD II INFORMATION The OBD II system can perform other tests and store other information that cannont be fully detailed in this booklet Among some of the other information stored when the vehicles MIL is illuminated showing air fuel ratio fuel trim fuel injector base pulse width loop status mass airflow rate engine speed engine load vehicle speed map sensor signal and engine cooling temperature This information is very helpful in fixing OBD II system faults For more information on OBD II systems consult the vehicles manufacturers service manual or a service publication like Mitchell Motor or ALLDATA PO400 PO401 PO402 PO403 PO404 PO405 PO406 PO407 PO408 PO410 PO411 PO412 PO413 PO414 PO415 PO416 PO417 PO420 PO421 PO422 PO423 PO424 PO430 PO431 PO432 PO433 PO434 PO440 PO441 PO442 PO443 PO444 PO445 PO450 PO451 PO452 PO453 PO454 PO455
21. em the reading will be 3 to 4 with the injection system activated If the O2 reading that the oxygen sensor picks up is incorrect air fuel ratio will be affected For CO2 you should consider that it is an excellent indicator of com plete engine combustion It is also produced by a functioning converter Usually the CO2 level before the catalytic converter will be about 11 to 12 If the con verter is functioning properly it will be 15 or higher out of the tail pipe Points to check when a vehicle fails testing 1 Was the vehicle running at operating temperature properly warmed up 2 Was the vehicle running at manufacturers specs 3 Is the vehicles cooling system operating properly 4 Is the vehicles EGR system functional 5 Does the vehicle have high mileage on the odometer 6 Has the vehicles engine or exhaust been modified 7 Make sure the vehicle is IM ready See the IM readiness cycle in the OBD II section Causes of test failure HC hydrocarbon failure Iginition misfire fuel system malfunction bad O2 senosr or other feedback sensor worn piston rings burned valves bad canister purge valve or system defect in PCV system inoperative converter CO carbon monoxide failure Improper air fuel mixture inoperative air injection sys tem inoperative choke cold idle enrichment device faulty O2 sensor or other feedback sensor incorrect timing inoperative converter NOX oxides of nitrogen failure Mechanic
22. es to maintain the air fuel ratio at 14 7 1 This is the air fuel ratio referred to as teh Stoichiometric Ratio Fuel trim information can be monitored through the Data Link with a scan tool The scan tool will monitor fuel trim in terms of percentage from 1 100 THE EVAPORATIVE EMISSIONS SYSTEM The EVAP system monitors tests for leaks in the Evaporative Emissions System The vehicles computer checks the EVAP which is the system where hydrocarbon vapors emitted from the gasoline or the fuel system are stored into a canister that is loaded with activated charcoal The system monitor is generally comprised of two components a purge valve and a fuel tank pressure sensor In most applications the monitor system will close the EVAP system off from the atmospheric pressure and will open the purge valve during vehicle cruise down The fuel pressure sensor in the fuel tank then checks the rate at which a vacuum increases in the EVAP system This information is then used by the vehicles computer to determine purge flow rate or volume Remember the func tion of this system is to store hydrocarbon vapors into the charcoal canister and then purge them into the engine generally through the intake manifold via a hose that con nects the two points The purge valve opens at the proper time to allow this to happen The EVAP monitor also checks the system for fuel leaks It does this by closing the purge valve completely which in turn causes the system to be compl
23. etely closed The pressure sensor in the fuel tank then checks the leak down rate If the rate is greater than the value stored in the vehicles computer a leak is determined to exist and the MIL will be illuminated The EVAP monitor is another Non Continuous Monitor THE EGR SYSTEM MONITOR The EGR monitor works by performing tests which open and close the EGR valve and measure the voltage signal sent by the EGR valves position sensor The computer com pares these signals to the ones that are stored in the computer and uses these figures to determine exhaust gas flow an efficiency If a problem is detected the MIL will illumi nate SECONDARY AIR INJECTION MONITOR This system checks the function of the secondary air injection system components The diverter valve and bypass valve are checked for proper function If the system uses an electronically drive air pump instead of the common engine belt driven type it checks this also The before converter oxygen sensors are used to check the exhaust to detect the excess oxygen that will be present in the exhaust This will determine if there is air flow from the air pump If a malfunction is indicated the MIL will illuminate MISFIRE MONITOR SYSTEM This system monitors and detects misfire on a cylinder by cylinder basis The system does this by using the crankshaft position sensor to detect a slowdown in crankshaft speed caused by a misfiring cylinder Not only can the system detect a misfir
24. gain Also make sure that the MIL bulb is good An ECM that shows the MIL to be commanded on but not illuminating the check engine light due to a bad bulb will fail an emission test even if everything else is correct Bulb replacement can be time consuming but it is necessary Consider the MIL bulb to be just another emission control and offer this service WHAT MAKES THE OBD II CATALYTIC CONVERTER DIFFERENT THAN A NORMAL OR NON OBD II CATALYTIC CONVERTER The main difference between the two is the oxygen storage capacity of the catalytic con verter The catalyst is comprised of three distinct parts 1 SUBSTRATE The structure onto which the catalytic reactants are deposited This structure is placed in contact with the exhaust gases The substrate can be in the form of pellets or a monolithic honeycomb It can also be metallic or ceramic 2 WASHCOAT This is a solution made up of alumina and other chemicals that stabi lize and promote a good catalytic reaction This coating of chemicals also extends the geometric surface area of the substrate This extending of the surface area is important because as this area is increased it allows for more space or sites in which a reaction can take place The more areas in which a reaction can take place the better the cata lytic reaction and the better the converter efficiency The catalytic washcoat also stores excess oxygen from lean operating cycles and releases it for use during rich cycles
25. gine It also monitors barometric pressure When this sensor fails it can cause a rich condition which can damage the converter Because testing of these sensors vary between make and model consult the manual before testing Generally there are two types the Voltage Type you would use a volt meter and a vacuum pump To check the Frequency Type you would use a tach and a vacuum pump CHARCOAL CANISTER AND PURGE VALVE This valve vents fuel vapors from the charcoal canister into the engine The vapors are collected into the charcoal CADIS from the fuel tank The cansister is located by the tank or under the hood 3 AIR INJECTION SYSTEM Air Pumps Air pumps operate from the vehicle engine through a belt This pump supplies the air injection needed at the catalyst and at the air manifolds Generally when this component goes bad it stops turning breaking its belts or it just becomes very noisy If the pump won t turn and the belt is broken off it is defective The air injection system as a whole aids in the control of carbon monoxide Air Manifolds Air manifolds direct air into the exhaust manifolds to aid in reduction of CO When they go bad it is usually obvious due to the loud exhaust noise coming from under the hood Check the air manifolds to make sure they are free of rust out or corrosion when cool High Temperature Hose This hose routes air from the air pump and diverter valve to the air manifolds and check valves If thi
26. idle speed or Ignition system malfunction CONVERTER MAUTE Vacuum leak Inoperative air pump or air nin injection Fuel system malfunction Cracked distributor cap Inoperative choke Engine mechanical damage Faulty coil Faulty PVC worn rings or burnt valves Faulty spark plug wires Improper timing Faulty 0 sensor Fouled plugs Faulty gas check valve Faulty Faulty canister purge valve Faulty rotor Faulty O sensor Overly rich fuel mixture Fuel system malfunction Faulty converter Faulty converter Faulty PVC valve Section Three OBD Il WHAT IS IT OBD II refers to the On Board Diagnostics generation two This is a system that has the ability to test its various components and systems and tell the driver when a fault has been detected that will cause the vehicle to put out excessive emissions This system first became available on passenger cars in the 1995 model year and 1996 for light trucks with a gross vehicle weight of under 8500lbs WHAT CAN THE SYSTEM DETECT The system has the ability to detect malfunctions in many engine systems that can cause excessive emissions Let s look at the individual system checks or monitors and how they work The OBD II system uses different monitors These monitors are divided into three types 1 Comprehensive Component Monitor 2 Continuous Monitor 3 Non Continuous Monitor The Comprehensive Component Monitor runs electrical tests on all of the se
27. ive it may be the cause of a converter failure Problems such as improper float adjustments air fuel mixture adjustments out of spec or worn metering rods can cause damage to the catalyst Also check the choke system to make sure it is operating properly and if the carburetor is an electronic feed back modle make sure all adjustments are made according to manufacturer specs Also make sure all feedback sensors and electronic components such as mixture con trol solenoids throttle position sensors and throttle holding solenoids are operating and are within specs FUEL INJECTION SYSTEM Problems in the fuel injection system can also cause problems with the converter Fuel injection systems differ greatly Basically a fuel injection system uses small electronical ly controlled solenoids that deliver or inject fuel into the throttle body or into the intake part of the engine These little solenoids are controlled by a computer which obtains information from various sensors located throughout the engine y These sensors help the computer to determine how much fuel to inject If an injector is leaking internally or dribbling fuel into the engine it may damage the converter If the oxygen sensor is defective or the map sensor is bad this can lead to converter damage Ifthe injection system uses a cold start injector which is a small injector that is used to richen theh mixture by injecting fuel into the intake air stream when the engin
28. ll need a scan tool to be able to decode or read DTCs CATCO offers an in expensive scan tool part T9035 and there are many others offered by a wide variety of sources When you connect the scan tool to the data link and turn it on it will display or read the stored DTCs These codes appear as such P0123 The first character in the display code identifies which system the code relates to B is used for body codes C is used for chasis codes P is used for powertrain codes The second character denotes what type of code it is O OBD II 1 Manufacturer 2or3 SAE The third character denotes what system the code refers to 1 or 2 denotes fuel or air 3 denotes ignition 4 denotes emission control 5 denotes speed control 6 denotes vehicle computer or output 7 or 8 denotes transmission 9 or O denotes SAE The fourth and fifth characters denote the part or condition that caused the problem The scan tools manual will identify the measuring of all displayed codes This explana tion is in a simple or abbreviated form and the scan tool manual vehicle service manual or competent diagnostic manual should be consulted for complete explanation of the OBD Il system The system may also have capabilitites to display enhanced DTC as opposed to just generic codes So again it is important to have not only proper tools but service manuals if you truly want to get to understand OBD II inside and out The DTCs are broken d
29. measures vehicle emissions for HC CO and NOX under a loaded condition The I M 240 is run on a Dynamometer It takes 240 seconds This procedure can show which vehicles are not meeting the emissions stan dards in a real and reliable way HOW OBD II EFFECTS I M 240 TESTING The OBD II system monitors emissions through its use of dedicated monitors to check for deteriorated or non functioning systems or controls It is very important that any vehicle taht comes into your shop under the following conditions gets its OBD II system checked thoroughly before the system is repaired and the vehicle is emission tested A Vehicle comes in with MIL illuminated B Vehicle comes in with a catalytic converter that is broken up internally C Vehicle has failed a State required emissions test D MIL commanded to be on through ECR but light is not illuminated After all repairs have been made trouble codes have been erased and the MIL has been turned off you will need to drive the vehicle before any emission tests can be performed The OBD II system conducts the tests under certain conditions or enabling criteria These conditions are comprised of various information a few examples 1 Elapsed time since vehicle engine start up 2 Throttle position 3 Engine speed 4 Vehicle speed 9 Engine temperature Most of the various systems tested by the different monitors are only conducted after the engine has reached normal operating temperature The c
30. nsors to ensure that they perform It tests the sensor range and also does rationality tests This test ensures that the sensor output makes sense or are rational when compared to each other NTK Sensor Shown Gray Wire Sensor Ground Probe Tip Black Wire Sensor Signal i a White Wire Heater Circuit Connector OXYGEN SENSOR SYSTEM MONITOR The O2 sensors are monitored or checked for proper reference signals and to make sure that the heater circuit is functioning O2 sensors that are located before the catalyt ic converter are tested for high and low voltage thresholds and for switching frequency the switching frequency test will count the number of times that the signal voltage goes beyond the mid point of 450 millivolts during a specified time frame and compares this figure with the information stored in the vehicles computer The system will also count the rich to lean transition and the lean to rich transition This again is checked against the time stored in the vehicles computer For universal O2 wiring information please see the O2 sensor section of this catalog THE CATALYTIC CONVERTER MONITOR The vehicles O2 sensors are used to determine catalytic converter efficiency All the ox ygen sensors located before the catalytic converter show a voltage pattern on an oscillo scope of a wave form having many peaks and valleys These peaks and valleys are the varying voltages of the oxygen sensor signaling rich and lean air fuel ratios
31. omputer runs three types of tests 1 PASSIVE TEST This test monitors a system component without affecting its opera tion 2 ACTIVE TEST The computer has the monitor produce a test signal so that its re sponse can be checked against stored information 3 INTRUSIVE TEST The computer performs system checks that affect vehicle perfor mance and emissions After a passive test is run and it fails the computer then performs active test procedures on the system If after this test a failure is found the computer will run an intrusive test If after the intrusive test produces a failure the computer may not store a trouble code and or illuminate the MIL unit after the failure appears in two consecutive tests Because of this it is suggested that you perform the drive cycle or I M Readiness Drive Cycle to be sure that all systems have been checked and that all I M Flags are set These are benchmarks or messages that the OBD Il system uses to show that all emis sion monitors have been run It is important that all of these I M Flags are set before the vehicle goes through an I M 240 test I M READINESS CYCLE A Vehicle should be started with the engine cold B Let vehicle idle until the engine is at normal operating temperature the engine cool ant temperature sensor should read 180 F or higher generally 5 to 10 minutes C Put vehicle in gear and idle for 45 seconds D Accelerate to 45mph with no more than a 1 4 throttle for 10 s
32. ousands of small channels through which the exhaust gas flows This piece of ceramic is treated with the washcoat and noble metals c METALLIC FOIL SUBSTRATE This type of substrate uses wound or stacked metal foil on to which the washcoat and noble metals are deposited The exhuast gas flows through this substrate This type has many advantages over ceramic such as being able to be made into shapes that cannot be easily done with ceramic d CERAMIC FOAM This type of substrate is composed of ceramic solution on foam It is then fired in a kiln to develop the mutli pore design seen in this photo This substrate is then treated with washcoat and noble metals As the exhaust gasses flow through it the catalytic reaction takes place In addition there are some other substrate designs that use screen metal foam wire wound elements and even ceramic fiber elements These types are currently not used in automotive applications 2 WASHCOAT This is a chemical formulation that is comprised of high surface area alumina and other compounds such as cerium zirconium nickel barium and lanthanum lts purpose is to extend the physical surface area of the substrate and to act as a surface onto which the noble metals are deposited It also acts to store the excess oxygen in the system so it can be used when needed 3 NOBLE METALS These are the commonly used elements platinum palladium and rhodium and are deposited onto the
33. own into 4 types Type 1 or type A indicates a DTC that is an emission related failure and illuminates the MIL after one trip in which the fault is detected Type 2 or type B indicates a DTC that is an emission related failure and illuminates the MIL after two trips in which the fault is detected Type 3 or type C indicates a DTC that is a non emission related failure and illuminates the MIL after one trip in which the fault is detected Type 4 or type D indicates a DTC that is a non emission related failure and illuminates the MIL after two consective trips in which the fault is detected See end of section for a list of emission related DTCs FIXED THE PROBLEM WHY WON T THE MIL GO OFF Once the MIL has come on it can be turned off with a scan tool The CATCO tool part 19035 will do this job easily The MIL should only be turned off after the problem that caused it is corrected Never disconnect the vehicles battery to try to shut the light off doing so can cause a host of new problems for the car owner and you Disconnect ing the battery can cause simple but aggravating problems such as a radio that will not work unless you know the security code to re enable it or a possible major problem like disconnecting and reconnecting the battery that causes a voltage surge which can dam age the vehicles computer The OBD Il system will reset and shut the MIL off if after three consecutive trips the fault does not occur a
34. rature Below Threshold Bank 2 Evaporative Emission Control System Malfunction Evaporative Emission Control System Incorrect Purge Flow Evaporative Emission Control System Leak Detected Small Leak Evaporative Emission Control System Purge Control Valve Circuit Malfunction Evaporative Emission Control System Purge Control Valve Circuit Open Evaporative Emission Control System Purge Control Valve Circuit Shorted Evaporative Emission Control System Pressure Sensor Malfunction Evaporative Emission Control System Pressure Sensor Range Malfunction Evaporative Emission Control System Pressure Sensor Low Input Evaporative Emission Control System Pressure Sensor High Input Evaporative Emission Control System Pressure Sensor Intermittent Evaporative Emission Control System Leak Detected Large Leak Fuel Level Sensor Circuit Malfunction Fuel Level Sensor Circuit Range Performance Fuel Level Sensor Circuit Low Input Fuel Level Sensor Circuit High Input Fuel Level Sensor Circuit Intermittent Purge Flow Sensor Circuit Malfunction PO466 PO467 PO468 PO469 PO470 PO471 PO472 PO473 PO474 PO475 PO476 PO477 PO478 PO479 Purge Flow Sensor Circuit Range Performance Purge Flow Sensor Circuit Low Input Purge Flow Sensor Circuit High Input Exhaust Pressure Sensor Malfunction Purge Flow Sensor Circuit Intermittent Exhaust Pressure Sensor Range Performance Exhaust Pressure Sensor Low Exhaust Pressure Sensor High Exhaust Pressure Sensor Intermi
35. re used Generally the EGR valve can be checked with a vacuum pump However some late 1970 s Ford EGR valves worked by air pressure supplied by the alr pump some EGR valves operate with positive or negative exhaust back pressure Also be aware taht some EGR valves are totally electronic Always consult a service manual for proper service and test procedures IDLE SPEED CONTROL MOTOR u This device helps the computer controlled engine to maintain proper idle speed When this device goes bad it can cause erractic idle speed stalling hesitation or engine run on This device can be checked with a 9 volt power source and an ohm meter Consult vehicle service manual i for proper wiring diagram and test procedure AIRTEMP SENSOR This sensor is sometimes called a Manifold Temperature sensor or an Air Charge Temperature sensor It monitors the temperature of the intake air and if defective it causes a problem of poor overall performance heavy black exhaust smoke and bad fuel economy Itis tested with an ohm meter COOLANT TEMPERATURE SENSOR This sensor is located on either the water outlet or the engine block It monitors engine coolant temperature The computer uses this information to control idle speed timing and fuel mixture If this sensor goes bad it can gt cause heavy black exhaust smoke surging or poor fuel economy To gt test this sensor with the engine cold disconnect the sensor wire harness With an ohm meter
36. red the charcoal canister will flood and the mixture will become very rich ANA and can damage the converter To check the valve disconnect the UA hoses to see if any gas comes out of the hoses or valve If there is gas the valve should be replaced AIR INJECTION SYSTEM Air Pumps Air pumps operate from the vehicle engine through a belt This pump supplies the air injection needed at the catalyst and at the air manifolds Generally when this component goes bad it stops turning breaking its belts or it just becomes very noisy If the pump won t turn and the belt is broken off it is defective The air injection system as a whole aids in the control of carbon monoxide Air Manifolds Air manifolds direct air into the exhaust manifolds to aid in reduction of CO When they go bad it is usually obvious due to the loud exhaust noise coming from under the hood Check the air manifolds to make sure they are free of rust out or corrosion when cool High Temperature Hose This hose routes air from the air pump and diverter valve to the air manifolds and check valves If this hose is found to be burnt check the exhaust check valve that is in that hose it may be defective Check Valves These valves allow air to pass to the various components ie air manifolds converter They should only allow the air to pass in one direction If air passes freely in both directions the diaphragm is ruptured and the valve is no good This failure can le
37. rket converter in the following situation A The vehicle is over 5 years old or has more than 50 000 miles This applies to vehicles produced in or before 1994 For vehicles 1995 or newer the period of 8 years or 80 000 miles applies B A state sponsored inspection program has determined that the current converter has been damaged or poisoned C Any situation where the need for converter replacement has been documented It is possible to use an aftermarket converter in a situation where the vehicle is less than 5 years old 1994 or older or has less than 50 000 miles These situations are A The catalytic converter is already missing from the vehicle and it has been properly documented B Astate inspection program has determined that the current converter is damaged or inoperable The following are examples of situations where original equipment converters must be installed A Vehicles O E converter is covered under a warranty or recall i B Vehicle has been returned from overseas use and the catalytic converter is missing
38. s A proper functioning catalytic converters downstream or after converter oxygen sen sor will show little or no fluctuation in voltage If catalytic converter degredation occurs affecting the oxygen storage capacity of the washcoat a fluctuating voltage signal will be sent to the vehicles computer which will in turn illuminate the MIL Malfunction lIl lumination Light This will notify the driver of a problem The vehicles computer has an algorithm stored in it which allows the computer to determine converter efficiency by the amount of oxygen obsorbed The catalyst monitor is a Non Continuous Monitor This type runs one time per drive trip THE FUEL SYSTEM MONITOR The fuel system monitor controls fuel trim to the engine The vehicles computer allows for fine tuning of the air fuel ratio The computer actually stores information on fuel trim and compares this to a pre programmed based fuel calculation Fuel trim can be divided into two types Long Term fuel trim and Short Term fuel trim The Short Term fuel trim applies to the function of temporary or short term changing of the fuel deliver Short Term fuel trim can only happen in closed loop operation Long Term fuel trim ap plies to the long term effects of the Short Term fuel trim corrections In simple terms the vehicles computer will add or subtract fuel from the programmed based calculation in accordance withe the signals received from the vehicles oxygen senors The computer tri
39. s hose is found to be burnt check the exhaust check valve that is in that hose it may be defective Check Valves These valves allow air to pass to the various components ie air manifolds converter They should only allow the air to pass in one direction If air passes freely in both directions the diaphragm is ruptured and the valve is no good This failure can lead to damage of the air pump diverter valve or the high temperature hose if left unchecked If hoses are melted or components like the air cin or rthe diverter valve are damaged check the exhaust check valves A ee Converter Air Tubes These tubes route air into the catalyst to help E24 aid in the oxidation process Check to make sure it is connected and D Al that it is not rusted through Sil DIVERTER VALVE This valve helps to route air to the exhaust manifold or catalytic converter to assist in maintaining proper emissions Operation should be checked and a manual should be consulted regarding proper test procedures EGR SYSTEM This system routes small amounts of exhaust gases back to the intake manifold to reduce oxides of nitrogen or NOX Systems vary by design so you need to consult the proper manual for the vehicle you are working on Some newer systems also use an EGR valve position sensor If the exhaust system you are working on has one it must be checked also While a bad EGR system will not lead to a converter failure it might be the reason why the
40. ttent Exhaust Pressure Control Valve Malfunction Exhaust Pressure Control Valve Range Performance Exhaust Pressure Control Valve Low Exhaust Pressure Control Valve High Exhaust Pressure Control Valve Intermittent Section Four Enhanced Testing IM 240 An enhanced testing procedure that lasts a total of 240 seconds The vehicle is tested on a roller or dynamometer This allows the car to be tested under varying loads and speeds This testing requires that the total exhaust produced during the test be analyzed instead of just a small sample as used in other tests The IM program that is administered by the state is intended to detect and repair in use vehicles with excessive emissions by encouraging the vehicles owner to properly maintain and use their vehicle The IM programs will encompass more areas as time goes on and will definately help to increase replacement of catalytic converters for shops doing exhaust and emissions work What does testing tell us The test paper that the IM 240 station gives the customer has some other information other than just HC CO and NOX You will also find O2 oxygen and CO2 carbon dioxide listed Generally O2 has an inverse relationship to CO meaning if one goes up or increases the other goes down or decreases Too little O2 during the combustion process will cause CO to increase The normal reading out of the tail pipe of O2 will be 1 5 or less If the car has a secondary air injection syst
41. u quickly accelerate the engine it will drop to zero When you release the throttle it will quickly return to its proper idle reading If there is a long delay in return of the proper vacuum reading it is a good indication of a restricted exhaust most likely a plugged converter THE TEMPERATURE TEST For this test you will need a digital pyrometer To commence testing run the vehicle at a high rpm for two minutes about 2000 rom This needs to be done to ensure that the converter has had time to activate Touch the probe of the pyrometer to the front of the converter and note temperature Touch the probe to the rear of the converter and note temperature There should be a noticeable difference between the two temperatures with the rear temperature being hotter If the rear temperature is not hotter than the front the converter is not working properly THE BACK PRSSURE TEST This test will require a back pressure gauge An inexpensive back pressure gauge can be made from a small pressure gauge that reads from 0 to 30 psi a piece of vacuum tubing and a small 1 8 O D piece of copper tube is inserted into A back pressure gauge may also be purchased from numerous sources pre made To use the back pressure gauge drill a 1 8 hole in the exhaust pipe at the front of each converter With the engine running check the back pressure The back pressure should be no more than 4 to 5 psi This reading is with the throttle partly open at 25
42. ulse Generator which generates its own signal through magnetic induction The third is the Optical Sensor This type uses a spinning wheel or rotor a light beam and a photo transistor As the wheel rotates and cuts through the light beam a signal is sent CAMSHAFT POSITION SENSOR This sensor signals camshaft position and speed and sends the signal back to the vehicles computer This sensor is of the same type that is used for crankshaft position OXYGEN SENSOR This sensor sends information to the ECU Electronic Control Unit to maintain proper air fuel mixture It is located either in the exhaust manifold pipe or j catalytic converter As an oxygen sensor operates it checks to see if oxygen is present in the system If no oxygen is detected this would indicate a rich mixture The oxygen sensor will read about 900mV B When excessive amounts of oxygen are present the sensor voltage will read about 100mV Rich mixture means high readings lean mixture means low readings Please note the exhaust temperature must be at least 600 degrees Farenheit for the sensor to operate The measurements should only be taken with a multimeter that has a 10 meg ohm impedence rating Failure to follow this rule may cause you to replace the vehicles ECU A properly functioning sensor will oscillate between 900mV and 100mV every few seconds You can measure this with your multimeter The reading does not oscillate or stays fixed the sensor is
43. vehicle has a NOX problem IDLE SPEED CONTROL This device helps the computer controlled engine to maintain proper idle N speed When this device goes bad it can cause erratic idle speed stalling A ae hesitation or engine run on This device can be checked with a 9 volt power Na eS source and an ohm meter Consult the vehicle service manual for proper wiring diagram and test procedure AIRTEMP SENSOR This sensor is sometimes called a Manifold Temperature sensor or an Air Charge Temperature sensor It monitors the temperature of the intake air and if defective it causes a problem of poor overall performance heavy black exhaust smoke and bad fuel economy It is tested with an ohm meter COOLANT TEMPERATURE SENSOR This sensor is located on either the water outlet or the engine block It monitors engine coolant temperature The computer uses this information 7 to control idle speed timing and fuel mixture If this sensor goes bad it can qm cause heavy black exhaust smoke surging or poor fuel economy To test M this sensor with the engine cold disconnect the sensor wire harness With an ohm meter measure the resistance across the sensor then reconnect the sensor harness and run the engine for 3 to 5 minutes until it reaches normal operating temperature Disconnect the wire harness and again measure resistance across sensor If the difference between cold and hot readings is less than 200 ohms the sensor is defective

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