Diagnostic Aids

AIR pump generally operates upon initial start-up before engine goes into closed loop fuel control. Some systems perform a passive diagnostic test at this time. See CONDITIONS FOR RUNNING . Active diagnostic test is performed after the engine goes into closed loop.

On vehicles that perform a passive test, the active test will only run if passive test fails or is indeterminate. If diagnostic test does not run, observe fuel trim correction. If fuel trim correction is more than +/- 4 percent, AIR system test may not run. If status does not update, test can be repeated until I/M system status updates to YES. See DIAGNOSTIC PROCEDURES .

I/M System Status does not indicate whether 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 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, emission related DTC portion of I/M system status display will indicate Malfunction Indicator Light (MIL) is requested.

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

I/M system status will update only when an emission related DTC fails for a second time, or when all tests pass. If an impending failure exists, system may require more time to run diagnostic than in set procedure. If test does not run after numerous attempts and no DTCs are set, review scan tool data list and service information for an indication of why test does not complete. See INSPECTION/MAINTENANCE SYSTEM CHECK .

Some tests may abort due to changes in conditions while test is running. Example: changes in engine load, such as cooling fan or 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.