Circuit/System Testing

Engine operating, move the related HO2S harnesses for the appropriate rear sensor between the HO2S harness connector and the engine control module (ECM) while monitoring the appropriate scan tool 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 of the appropriate HO2S.
Ignition ON, verify the scan tool HO2S parameter is between 350-500 mV.
- If greater than 500 mV, test the signal circuit of the HO2S sensor for a short to voltage. If the circuit/connections test normal, replace the ECM.
Verify that none of the following conditions exist:
- Rich fuel injectors-Refer to FUEL INJECTOR BALANCE TEST WITH SPECIAL TOOL or FUEL INJECTOR BALANCE TEST WITH TECH 2 .
- Water intrusion in the HO2S harness connector
- 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) .
- A collapsed air intake duct
- 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/connections test normal, replace the applicable HO2S.