Evaporative Emission Test Won’t Run

Posted 02/01/2013
By Dave Martin

Have you ever noticed that the last emission monitor to run is often the evaporative system? Many technicians believe if the monitor won’t run in 10 miles, then drive 100 miles. Unfortunately, it doesn’t work that way. You can drive 500 miles but if the correct conditions are not met, the test won’t run; it will never run. So, if you don’t want to join the 100-mile club, read on.

The test is divided into two areas: 1) Pretest enable criteria, and 2) Emission system test.

To set up the pretest enable criteria:

1. Look up the emission test requirements and make note of each condition that must occur before the test will run.
2. Along with these items, there will be codes associated with the particular emission test. Look up the Inspection/Maintenance (I/M) System DTC Table for that list of codes.
3. Then look up the enable criteria for each of those codes. Usually, but not always, the enable criteria for the code test is the same as the items listed in the main emission test set. All of these criteria have to be met to get the actual test to run.

A common “show stopper” is the outside ambient temperature. If the ambient temperature is not within the listed range, the solution is to simply wait for the temperature to change. This often means waiting for a new season. That’s right; many weeks may go by before the evaporative test will be allowed to run. This also means that the system repair you just completed won’t be tested either. You may not know for several weeks if the work that was done actually fixed the problem.

After all criteria have been met, the actual test of the evaporative system can now occur. Make note of the driving conditions that are required to complete the test and follow them. Remember that when the emission test is completed, it results in either a “pass” or a trouble code – this could be months after the repair was made.

If this process gets hung up and won’t complete, connect your scanner and recheck the code section, “Not Ran Since Code Cleared.” Review the criteria the computer needs to see to complete the running of those remaining codes. Get the conditions right and the system will complete the test.

Finally, there are some vehicles that, for whatever reason, won’t move through the process. If everything has been done according to requirements, try a reflash of the PCM, or if that does not work, replace it. If you have any questions, give us a call.

Dave Martin is an Identifix GM specialist. He is an ASE Master with L1 certification.

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