The purpose of this test is to satisfy the enable criteria that are necessary in order to execute the I/M readiness diagnostics for the Heated Oxygen Sensor (HO2S) System. The test may be used in order to set the I/M System Status to YES. Before you perform this test, ensure that the vehicle meets the requirements listed in the Conditions for Running. Failure to meet the necessary requirements may produce inaccurate test results.

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

The I/M System Status does not indicate whether the test has passed or failed, only that a decision was made. When all of the diagnostics for a specific system have run and passed, the 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 the malfunction indicator lamp (MIL) is requested. The I/M System Status also registers the number of diagnostic trouble codes (DTCs).

The first failure of a type B DTC does not constitute a final determination of pass or fail, and will not update the I/M System Status to YES. A second trip is required, and all the conditions to run must be met in order for the test to run again. 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 of the tests pass.

If there is an impending failure, the system may require more time to run the diagnostic than was allotted in the set procedure. If the test does not run after numerous attempts and no DTC is set, review the appropriate scan tool data list and the 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, maintain necessary enable conditions until the system status updates to YES.

The numbers below refer to the step numbers on the diagnostic table.

1. Before performing this test, perform the I/M System Check. Failure to do so may result in difficulty updating the status to YES.

2. Preprogramming the scan tool will reduce the time that the oxygen sensor heaters operate while verifying the enable criteria.

3. This step identifies a first failure of a type B DTC. A DTC only appears on the I/M System Status display when the DTC becomes a MIL-illuminating DTC. This occurs on the second failure of a type B DTC. A first failure of a type B DTC will not allow the I/M System Status to update to YES. Refer to Diagnostic Aids.

4. This step helps to identify any unique or unusual criteria that are required in order to run the diagnostic test if the universal set procedure does not. This information is in the Conditions for Running the DTC.

5. The I/M System Status only reports on whether a diagnostic has run, not the outcome of the test. If any emission related DTC sets after the tests are complete, the DTC will require diagnosis.