Diagnostic Aids

HO2S heater tests will normally run within 2 minutes allotted in procedure. If there is an indeterminate condition, test may take up to 8 minutes on some vehicles before a decision of pass or fail is made. If test does not update within allotted period of time, continue operation within enable conditions until test updates to YES. If test does not update to YES, it may have failed or aborted due to loss of enabling conditions. Extremely high ambient temperatures may prevent HO2S heater test from initiating.

I/M SYSTEM STATUS does not indicate whether test has passed or failed, only that test was 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.

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.