Part 4. OBDII "Trouble Code" Test: This OBDII test is not applicable to 1995 and older vehicles. Trouble codes indicate that the OBD II computer has detected a problem within the emissions system. The trouble code will specifically indicate the component and problem which was found. Newer vehicle's have very complex codes in the thousands. Smog check repair centers can retrieve the trouble codes from the OBDII and inspect the component/s which the codes indicate.

OBD-II Trouble Code Lookup - How to extract trouble codes using a trouble code scanner, and what do the codes mean?

What if I Fail the Check Engine Light Test? There are three ways your car may fail the check engine light test. You may fail in one or all three of the categories below.

Failure A. Check engine light, malfunction indicator lamp or service engine soon light illuminated, and smog technician enters this information into the smog machine.

- Repair for Failure A. Using a trouble code scanner, the smog technician must extract the trouble codes causing the check engine light to illuminate, and diagnose the responsible emissions components hands-on. Once problem/s are repaired, the vehicle must be driven to set proper readiness flags, and can then be retested.

Failure B. Smog machine detects an active OBD-II trouble code during the smog test via the OBD-II data link connecter. Check engine light is not currently illuminated, but may have been in the past.

- Repair for Failure B. After the smog test is complete the smog technician will hand over a Vehicle Inspection Report or VIR. The VIR will have printed at the bottom the trouble code/s which were extracted by the smog machine. The smog technician must use these code/s the conduct a hands-on diagnosis of the components in question. Usually a diagnose fee of two labor hours will be required. Average labor rate is $65.00 per hour.

Note: The trouble code/s will only direct the smog technician to the general area of the system failure. It is up to an emissions repair mechanic to inspect the system and emissions components for proper operation, and repair faults as necessary.

Failure C. Smog machine detects certain required "readiness flags" are not set. The reason for the flags not being set depends on the select readiness flag. Two possibilities apply for all readiness flag test failures:

Recent disconnection of battery (12v) system. This is common on vehicles which have recently required removal or disconnections of the vehicle's battery or engine control computer.
Vehicle has an emissions system failure not allowing "readiness flag" self tests to run.

- Repair for Failure C. If readiness flags are not set because your car's battery was recently disconnected, and your car's malfunction indicator lamp, check engine light, or service engine soon light is not illuminated, the repair might be simple. Drive your vehicle for one week under normal driving conditions. During this period the emissions computer will run the proper readiness self tests to set the required "readiness flags". Your vehicle should not pass the smog check.

If this does not resolve the issue, or if the check engine light is illuminated, a more severe emissions failure may exist, requiring hands-on diagnosis by a smog check certified smog repair center.