Diagnostic Aids

The PCM runs a maximum of 6 tests per trip until the catalyst system status updates to YES. If the status does not update, the test outlined in this procedure can be repeated until the I/M system status updates to YES. The I/M system status does not indicate whether the test has passed or failed, only that a decision was made. When all of the diagnostics for a specific system have run and passed, the I/M system status updates to YES. If a test for a specific system has failed, the I/M system status updates to YES, indicating a determination was made, even if all of the required tests have not run. When a failure occurs, the emission related DTC portion of the I/M system status display indicates the malfunction indicator light is requested. The I/M system status also registers the number of DTCs.

First failure of a type "B" DTC does not constitute a final determination of pass or fail, and will not update I/M system status to YES. A second trip is required, and all conditions to run must be met in order for test to run again. These conditions may include a partial or complete engine cool down. I/M system status will update only when DTC fails second time, or if all tests pass.

If there is an impending failure, system may require more time to run diagnostic than was allotted in set procedure. If test does not run after numerous attempts and no DTC is set, review appropriate scan tool data list and service information for an indication of why test does not complete. Some tests may abort due to changes in conditions while test is running. For example, changes in engine load, such as a cooling fan or an A/C compressor clutch turning on, may cause test to abort.

If a diagnostic test is difficult to run, observe I/M system status display while maintaining necessary enable conditions until system status updates to YES.