Circuit/System Testing

Verify that none of the following conditions exist:
- Inspect the HO2S 1 and HO2S 2 for being secure
- Damaged wiring between either HO2S and the ECM
- Leaking fuel injectors-Refer to Fuel Injector Balance Test with Special Tool or Fuel Injector Balance Test with Tech 2
- High fuel system pressure-Refer to Fuel System Diagnosis
- Fuel that is contaminated-Refer to Alcohol/Contaminants-in-Fuel Diagnosis (w/o Special Tool) or Alcohol/Contaminants-in-Fuel Diagnosis (w/ Special Tool)
- Contaminated HO2S-Silicon
- If you find any of the above conditions, repair as necessary.
Ignition OFF, disconnect the harness connector at the HO2S 2.
Ignition ON, verify the scan tool HO2S 2 voltage parameter is between 350-550 mV.
- If greater than the specified range, test the HO2S 2 high signal circuit for a short to voltage. If the circuit/connections test normal, replace the ECM.
Connect the harness connector at the HO2S 2.
Engine idling, raise the engine speed above 1,200 RPM for 30 seconds. Verify the scan tool HO2S 2 voltage parameter is less than 1,000 mV.
- If greater than the specified range, replace the HO2S 2.
Engine idling, move the HO2S 1 and HO2S 2 harnesses between the HO2S harness connector and the ECM. Observe the scan tool HO2S 1 lambda parameter, and the HO2S 2 voltage parameter. Verify neither parameter changes abruptly.
- If the parameter changes abruptly, repair the harness/connections as necessary.
If all circuits/connections test normal, replace the HO2S 1.