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 the 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 a decision was made. 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, emission related DTC portion of 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 an emission related DTC fails 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 the 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.