Diagnostic Aids

The control module only runs the EGR active tests during a gradual deceleration with a closed throttle and vehicle speed greater than 25 MPH. Several deceleration cycles may be necessary in order to accumulate a sufficient number of EGR flow samples. The procedure outlined is for a clear, flat road. If procedure is performed on a road with a slight downhill grade, test may acquire the necessary sample counters in one or 2 decel trips. If test is interrupted during the procedure, it may take more than 3 deceleration cycles to complete the test. If status does not update, the test in this procedure can be repeated until the I/M system status updates to YES.

I/M system status does not indicate whether test has passed or failed, only that test has run. 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, DTC portion of the I/M system status display will indicate MIL is requested. I/M system status also registers 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 to complete engine cool down. I/M system status will update only when DTC fails second time, or 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 the 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.