Circuit/System Testing

Engine idling, move the related HO2S harnesses for the rear sensor between the HO2S harness connector and the engine control module (ECM) while monitoring the appropriate HO2S voltage parameter. Verify that the HO2S parameter does not change abruptly while moving the related harnesses.
- If the HO2S parameter does change abruptly while moving the related harnesses repair the circuit as necessary.
Ignition OFF, disconnect the harness connector at the rear HO2S.
Engine idling, verify that the HO2S parameter is between 350-550 mV.
- If greater than the specified range, test the HO2S high signal circuit for a short to voltage. If the circuit tests normal, replace the ECM.
- If less than the specified range, test the HO2S high signal circuit for a short to ground. If the circuit tests normal, replace the ECM.
Verify that none of the following conditions exist:
- Rich fuel injectors-Refer to Fuel Injector Balance Test with Special Tool
- Water intrusion in the HO2S harness connector
- High fuel system pressure-Refer to Fuel System Diagnosis
- Fuel that is contaminated
- A restricted air filter element
- Exhaust system restrictions
- Excessive fuel in the crankcase
- An engine mechanical condition-Refer to Symptoms - Engine Mechanical
- If you find any of the above conditions, repair as necessary.
If all circuits test normal, replace the HO2S2.