Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Diagnostic Aids
The HO2S heater tests will normally run within the 2 minutes allotted in the 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 the 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 the loss of enabling conditions. Extremely high ambient temperatures may prevent HO2S heater test from initiating.
The I/M System Status does not indicate whether test has passed or failed, only that a decision was made. When all of the 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 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 that MIL is requested. The I/M System Status also registers the 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, observe the I/M System Status display while maintaining the necessary enable conditions until the system status updates to YES.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.