Diagnostic Aids

Extreme high or low ambient temperatures may prevent EVAP system tests from initiating. Performing a visual inspection prior to running EVAP system set procedure may prevent having to repeat the test. A loose fuel cap may cause a test to abort or fail and prevent I/M system status from updating. A failed or aborted test will require the vehicle to cool down to meet enable criteria to run another test.

I/M system status does not indicate whether the test has passed or failed, only that a decision was made. When all diagnostics for a specific system have run and passed, I/M system status will update to YES. If a test for a specific system has failed, I/M system status will update to YES, indicating a determination was made, even if all required tests have not run. When a failure occurs, the emission related DTC portion of the I/M system status display will indicate the Malfunction Indicator Light (MIL) is requested. I/M system status also registers the number of DTCs.

The 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 for the test to run again. These conditions may include a partial to complete engine cool down.

The I/M system status will update only when an emission related DTC fails the second time, or when all tests pass.

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

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