Diagnostic Aids

Powertrain Control Module (PCM) only runs EGR active tests during a gradual deceleration with closed throttle and vehicle speed more than 25 MPH. Several deceleration cycles may be necessary to accumulate a sufficient number of EGR flow samples. Procedure is designed for a clear, flat road. If procedure is performed on a road with a slight down hill grade, test may acquire necessary sample counters in one or two decel trips. If test is interrupted during the procedure, it may take more than three deceleration cycles to complete the test. If status does not update, test can be repeated until I/M system status updates to YES.

I/M system status does not indicate if test has passed or failed, only that a decision was made. When all of diagnostics for 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, emission related DTC portion of 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 test to run again. See CONDITIONS FOR RUNNING . 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, 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.