Diagnostic Aids

AIR pump generally operates once per ignition cycle, usually upon initial start up before engine goes into closed-loop. The active test is performed after engine goes into closed-loop and will only run if passive test fails. The active test may not run if passive test passes.

If diagnostic test does not run, observe fuel trim correction. If fuel trim correction is more than plus or minus 4 percent, the AIR system test may not run. If status does not update, 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 test has passed or failed, only that a decision was made. When all of the 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, the I/M system status will update 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 will indicate MIL is requested. The I/M system status also registers the number of DTCs.

The I/M system status will update only when DTC fails the second time, or all of the tests pass. If there is an impending failure, system may require more time to run the diagnostic than was allotted in the 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 the test does not complete. 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 the I/M system status display while maintaining the necessary enable conditions until the system status updates to YES.