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OBD 2 represents the latest in Automotive and Emissions Control Technology.
All 1996 and newer passenger cars and light trucks are equipped with the OBD 2 technology. OBD II requires that the on-board computer monitors and actively performs diagnostic tests on vehicle power train and emissions related systems. By properly maintaining your OBD II vehicle, you are insuring peak performance, optimal gas mileage, and minimal emissions.
How is an OBD II emissions test different?
Emissions tests on 1995 and older vehicles consist of sampling the exhaust to measure the percentage of emissions emitted by the vehicle. OBD II equipt vehicles constantly test themselves. During an OBD II emissions inspection, certified test equipment recieves test results from the vehicle's OBD II computer.
What is the M.I.L.?
A Malfunction Indicator Lamp must illuminate to alert the driver if a system or component either fails or deteriorates to the point where the vehicle emissions could rise above 1 1/2 times the federal test standards. federal Emissions Standards should not be compared to existing tail pipe standards used to determine Pass/Fail for vehicles 1995 and older!
The MIL is located in the instrument cluster and must illuminate when the key is turned on and, unless a problem exists, will extinguish when the engine is started. If the MIL does not illuminate when the key is turned on, or remains on after the engine is running, the problem must be repaired as soon as possible. With Key On Engine Off (K.O.E.O.), some MILs illuminate only momentarily.
Which light is the MIL?
Automobiles use a variety of warning lamps to notify drivers of different conditions. However, in the case of emissions M.I.L., the phrase "Service Engine Soon" or "Check Engine" or an I.S.O. symbol may be substituted.
What does the flashing MIL mean?
If the MIL flashes or blinks while the engine is running, the OBD II system has detected a problem that could result in serious damage to the engine and/ or emissions control systems. The vehicle should be repaired immediately!
How does the MIL work?
Let's look deeper how all this works:
There is a number of sensors that provide the ECM with all necessary inputs such as the engine temperature, ambient temperature, vehicle speed, load, etc. According to these inputs, the ECM makes initial adjustments adding or subtracting fuel, advancing or retarding the ignition timing, increasing or decreasing idle speed, etc.
There is a primary (upstream) oxygen sensor installed in the exhaust before catalytic converter that monitors the quality of combustion in the cylinders. Based on the feedback from this oxygen sensor the ECM makes further adjustments to the air-fuel mixture to further reduce emissions.
There is another, secondary (downstream) oxygen sensor installed after catalytic converter in the exhaust that monitors catalytic converter's efficiency.
Besides, there are few additional emission control related vehicle systems. For example, there is an Evaporative system (EVAP), designed to prevent gasoline vapors from the gas tank from being released into the atmosphere. It also contains a number of sensors and actuators controlled by the ECM.
The ECM has self-diagnostic capability and constantly tests operation of all sensors and components. When any of the sensor signals is missing or out of normal range, the ECM sets a fault and illuminates the "Check Engine" or "Service Engine Soon" light also called MIL (Malfunction Indication Light) storing the corresponding Diagnostic Trouble Code (DTC) in the ECM memory.
The same will happen if a mechanical component of controlled system fails. For example, if the EGR valve fails, this will also cause the "check engine" light to come on. Even a loose gas cap will cause the "check engine" to come on - the ECM constantly checks if the gas tank is sealed properly.
To sum up, the "Check Engine" or "Service Engine Soon" light comes on when there is a problem with any emission-related component or system. The stored trouble code can be retrieved with the special scan tool by the technician. The code itself does not tell exactly which part to replace, it only gives a direction where to look for - the technician has to perform certain tests specific for each code to find the exact cause of the problem.
What is a trouble code?
Whenever the OBD II system detects a problem, the system will store a trouble code which is directly related to the compotent in which the fault was detected. The trouble codes assist technicians in diagnosing and repairing the OBDII system.
This picture represents the various sensors in the OBD II system.
What is a system readiness flag?
The OBD II system must run a series of self tests. The readiness flags indicate whether the self tests have or have not run successfully. The emissions test cannot continue until all EPA required self tests have successfully run. Readiness flags will not reset to not ready if: (1) a trouble code has been erased; (2) the battery goes dead; or (3) the battery has been disconnected.
How do I pass an OBD II emissions test?
1. The vehicle must be able to communicate with the test equipment.
2. The MIL must be able to pass a bulb function test.
3. Readiness flags must be set to READY as required by EPA for the correct model year.
4. The MIL cannot be commanded on by the vehicle's PCM (computer) with the engine running.
5. All anti-tampering requirements must be met.
What if my vehicle fails the OBD II test?
If the MIL is on and diagnostic codes are detected, the vehicle must be repaired before a certificate will be issued. Contact your dealer to determine if your vehicle is under warranty.
Be sure to see the Guide Reasons for catalytic converter failure.
Bear River Converters
We are the catalytic converter experts!
Selling superior quality converters, flex pipe, and stainless tips.
Check out our eBay store!
We carry an extensive line of premium quality converters. If you need a converter, we will get it for you!
This guide was written by Bear River Converters, the catalytic converter experts. To find a complete line of premium quality converters, flex pipe, and stainless steel tips, visit our eBay store here.
To contact us:
Bear River Converters
1877 W. Park Avenue
Riverton, UT 84065
Web: www.bearriverconverters.com
Phone: 888-782-8825 (Toll Free)
Fax: 801-446-4511
E-mail: brc@bearriverconverters.com
All 1996 and newer passenger cars and light trucks are equipped with the OBD 2 technology. OBD II requires that the on-board computer monitors and actively performs diagnostic tests on vehicle power train and emissions related systems. By properly maintaining your OBD II vehicle, you are insuring peak performance, optimal gas mileage, and minimal emissions.
How is an OBD II emissions test different?
Emissions tests on 1995 and older vehicles consist of sampling the exhaust to measure the percentage of emissions emitted by the vehicle. OBD II equipt vehicles constantly test themselves. During an OBD II emissions inspection, certified test equipment recieves test results from the vehicle's OBD II computer.
What is the M.I.L.?
A Malfunction Indicator Lamp must illuminate to alert the driver if a system or component either fails or deteriorates to the point where the vehicle emissions could rise above 1 1/2 times the federal test standards. federal Emissions Standards should not be compared to existing tail pipe standards used to determine Pass/Fail for vehicles 1995 and older!
The MIL is located in the instrument cluster and must illuminate when the key is turned on and, unless a problem exists, will extinguish when the engine is started. If the MIL does not illuminate when the key is turned on, or remains on after the engine is running, the problem must be repaired as soon as possible. With Key On Engine Off (K.O.E.O.), some MILs illuminate only momentarily.
Which light is the MIL?
Automobiles use a variety of warning lamps to notify drivers of different conditions. However, in the case of emissions M.I.L., the phrase "Service Engine Soon" or "Check Engine" or an I.S.O. symbol may be substituted.
What does the flashing MIL mean?
If the MIL flashes or blinks while the engine is running, the OBD II system has detected a problem that could result in serious damage to the engine and/ or emissions control systems. The vehicle should be repaired immediately!
How does the MIL work?
Let's look deeper how all this works:
There is a number of sensors that provide the ECM with all necessary inputs such as the engine temperature, ambient temperature, vehicle speed, load, etc. According to these inputs, the ECM makes initial adjustments adding or subtracting fuel, advancing or retarding the ignition timing, increasing or decreasing idle speed, etc.
There is a primary (upstream) oxygen sensor installed in the exhaust before catalytic converter that monitors the quality of combustion in the cylinders. Based on the feedback from this oxygen sensor the ECM makes further adjustments to the air-fuel mixture to further reduce emissions.
There is another, secondary (downstream) oxygen sensor installed after catalytic converter in the exhaust that monitors catalytic converter's efficiency.
Besides, there are few additional emission control related vehicle systems. For example, there is an Evaporative system (EVAP), designed to prevent gasoline vapors from the gas tank from being released into the atmosphere. It also contains a number of sensors and actuators controlled by the ECM.
The ECM has self-diagnostic capability and constantly tests operation of all sensors and components. When any of the sensor signals is missing or out of normal range, the ECM sets a fault and illuminates the "Check Engine" or "Service Engine Soon" light also called MIL (Malfunction Indication Light) storing the corresponding Diagnostic Trouble Code (DTC) in the ECM memory.
The same will happen if a mechanical component of controlled system fails. For example, if the EGR valve fails, this will also cause the "check engine" light to come on. Even a loose gas cap will cause the "check engine" to come on - the ECM constantly checks if the gas tank is sealed properly.
To sum up, the "Check Engine" or "Service Engine Soon" light comes on when there is a problem with any emission-related component or system. The stored trouble code can be retrieved with the special scan tool by the technician. The code itself does not tell exactly which part to replace, it only gives a direction where to look for - the technician has to perform certain tests specific for each code to find the exact cause of the problem.
What is a trouble code?
Whenever the OBD II system detects a problem, the system will store a trouble code which is directly related to the compotent in which the fault was detected. The trouble codes assist technicians in diagnosing and repairing the OBDII system.
This picture represents the various sensors in the OBD II system.What is a system readiness flag?
The OBD II system must run a series of self tests. The readiness flags indicate whether the self tests have or have not run successfully. The emissions test cannot continue until all EPA required self tests have successfully run. Readiness flags will not reset to not ready if: (1) a trouble code has been erased; (2) the battery goes dead; or (3) the battery has been disconnected.
How do I pass an OBD II emissions test?
1. The vehicle must be able to communicate with the test equipment.
2. The MIL must be able to pass a bulb function test.
3. Readiness flags must be set to READY as required by EPA for the correct model year.
4. The MIL cannot be commanded on by the vehicle's PCM (computer) with the engine running.
5. All anti-tampering requirements must be met.
What if my vehicle fails the OBD II test?
If the MIL is on and diagnostic codes are detected, the vehicle must be repaired before a certificate will be issued. Contact your dealer to determine if your vehicle is under warranty.
Be sure to see the Guide Reasons for catalytic converter failure.
Bear River Converters
We are the catalytic converter experts!
Selling superior quality converters, flex pipe, and stainless tips.
Check out our eBay store!
We carry an extensive line of premium quality converters. If you need a converter, we will get it for you!
This guide was written by Bear River Converters, the catalytic converter experts. To find a complete line of premium quality converters, flex pipe, and stainless steel tips, visit our eBay store here.
To contact us:
Bear River Converters
1877 W. Park Avenue
Riverton, UT 84065
Web: www.bearriverconverters.com
Phone: 888-782-8825 (Toll Free)
Fax: 801-446-4511
E-mail: brc@bearriverconverters.com
Guide created: 01/29/07 (updated 06/19/09)
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