OBDII FAQ

What does my Diagnostic Trouble Code (DTC) mean?
Each DTC indicates the type of fault and the area of the OBD-ii and power train/emission control system where the fault is located. When a problem occurs which may cause the vehicles emissions to exceed applicable standards, the OBD-ii system identifies the failure with a specific DTC, illuminates the malfunction indication light (MIL) and records a record of what has occurred. The link provided below contains a reference list of codes associated with OBD-ii, specifically related to emission system repairs.

How does OBD-II work?
The computer continuously tracks and stores information about the vehicle”s performance. The on-board computer turns on the “check engine” or “service engine soon” light if it finds a problem with the vehicle’s emission control system
What are the advantages of using the OBD-II inspection?
OBD II identifies the causes for a vehicle to fail its emissions test. By issuing specific diagnostic codes, OBD-II pinpoints the problem, allowing repair technicians to make quicker, more effective repairs. This saves time and money. OBDII is an early warning system that alerts vehicle owners to emissions problems at a stage where repairs are less costly and perhaps even under warranty. OBD II inspections also are quicker than previous tests. Newer vehicles operate cleaner due to improved technology and sophisticated emission control systems, but these systems must be in proper working order for the vehicle emissions to remain low. When an engine is not running as designed, performance is lost, fuel is wasted and air pollution increases. OBD II can detect problems drivers do not. By detecting emissions control deterioration and/or failures, and alerting the driver to the need for attention, vehicles can be properly serviced before more serious problems develop.
How can my vehicle fail an OBD-II test?
Your vehicle will fail the OBD-II test if the Malfunction Indicator Lamp (Check Engine) light is illuminated.

For 1996 – 2000 light duty gasoline vehicles (not more than 10,500 lbs. GVWR), if more than 2 supported readiness monitors are not set (not ready), the OBD test cannot be completed. If the vehicle originally failed for catalyst failure (visual or diagnostic trouble code), then the catalyst monitor must pass the readiness test.

For 2001 and newer light duty gasoline vehicles (not more than 10,500 lbs. GVWR), if more than 1 supported readiness monitor is not set (not ready), the OBD test cannot be completed. If the vehicle originally failed for catalyst failure (visual or diagnostic trouble code), then the catalyst monitor must pass the readiness test.

Readiness monitors must be set before a vehicle returns for a retest. If the supported monitors are not ready, then the vehicle will fail the OBD-II test.

If your check engine light fails to illuminate at Key On, Engine Off (KOEO) your vehicle will fail the OBD-II test.
My vehicle failed only for Monitor Readiness that read “not ready”

The computer in your vehicle performs diagnostic tests on certain emissions systems while you are driving. These system monitors are usually set (ready or complete). Sometimes system monitors become “not ready” due to a problem with your vehicle, the battery in your vehicle having been disconnected or the computer having had its memory erased.

For 1996 – 2000 light duty gasoline vehicles (not more than 10,500 lbs. GVWR), if more than 2 supported readiness monitors are not set (not ready), the OBD test cannot be completed. If the vehicle originally failed for catalyst failure (visual or diagnostic trouble code), then the catalyst monitor must pass the readiness test.

For 2001 and newer light duty gasoline vehicles (not more than 10,500 lbs. GVWR), if more than 1 supported readiness monitor is not set (not ready), the OBD test cannot be completed. If the vehicle originally failed for catalyst failure (visual or diagnostic trouble code), then the catalyst monitor must pass the readiness test.

Readiness monitors must be set before a vehicle returns for a retest. If the supported monitors are not ready, then the vehicle will fail the OBD-II test.
What is a readiness monitor?
1996 and newer light-duty vehicles have built-in monitoring systems that can detect when emissions control systems have a fault that may cause excess emissions. These monitoring systems perform various checks under certain operating conditions and also give an indication of whether those checks have been performed or not. These indicators are called readiness monitors.If any of the readiness monitors are Not Ready, that means that the system cannot provide a complete picture of the vehicle’s emissions control system health. Resolving this situation requires that the vehicle be operated under the circumstances prescribed by the manufacturer that will allow all of the necessary self–diagnostic checks to complete. See your repair center for more specific information.If all readiness monitors are set to Ready, that means that the various emissions control systems have been tested and the OBD system can provide a complete picture of the overall emissions control system health.
Re-setting an Illuminated Check Engine Light or Malfunction Indicator Lamp (MIL)
An illuminated MIL is your vehicle’s way of telling you it has found a problem related to the emissions control or engine management systems. Take it to a repair technician to have the problem addressed before it becomes more serious.Temporarily disconnecting the car battery or re-setting your vehicle’s computer memory with a scan tool may temporarily turn the MIL off; however, this will also set the status of the On-Board Diagnostic readiness monitors to Not Ready. The status remains Not Ready until the vehicle’s computer checks the components to determine if they are operating properly. After the check is run, the monitors are set to Ready. Your vehicle will fail the OBD inspection if the OBD system has not performed enough readiness checks.
What should I do if my vehicle failed?

You should have your vehicle serviced by a qualified technician. You are free to select a qualified repair technician or repair the vehicle yourself. However, due to the complexity of today’s vehicles, you should strongly consider having your vehicle repairs performed by a qualified technician who is experienced in diagnosing and repairing vehicle emissions systems.

What should I do if my vehicle’s “Check Engine” light is flashing on and off?
If the Check Engine light is flashing or blinking, you should have your vehicle serviced as soon as possible. The flashing light may indicated that there is an engine misfire, and extensive driving with an engine misfire could damage your vehicle’s catalytic converter.
Any tips I should follow before I get my vehicle inspected?
Yes. Some vehicles require extensive driving to reset certain system readiness monitors. Do not disconnect the battery on your vehicle. If your vehicle is in for service, ask your technician NOT to clear the computer’s memory since this will only unset the system readiness monitors and result in your vehicle failing the OBD-II test. Also, be sure your vehicle is at normal operating temperature when you arrive at the test center.

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