Circuit/System Testing

Verify that none of the following conditions exist:
- An exhaust leak near the HO2S-Refer to Symptoms - Engine Exhaust .
- Lean or rich fuel injectors-Refer to Fuel Injector Balance Test with Special Tool .
- The HO2S is not securely installed.
- Water intrusion or corrosion in the HO2S harness connector
- Poor terminal tension at the HO2S and at the ECM.
- HO2S wiring harness damage
- Low or high fuel system pressure-Refer to Fuel System Diagnosis .
- Fuel that is contaminated-Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
- Fuel saturation of the EVAP canister
- Engine vacuum leaks
- Incorrect RTV sealant
- Engine oil consumption-Refer to Symptoms - Engine Mechanical .
- Engine coolant consumption-Refer to Loss of Coolant .
- If you find any of the above conditions, repair as necessary.
Ignition OFF, disconnect the harness connector of the heated oxygen sensor (HO2S) 2.

IMPORTANT: The test lamp is used to load the circuit and may not illuminate.

Connect a test lamp between the low reference circuit of the HO2S 2 and the positive terminal of the battery.
Ignition ON, test for less than 0.1 volt between the low reference circuit of the HO2S and ground.
- If greater than 0.1 volt, test the low reference circuit of the HO2S for a short to voltage or an open/high resistance. If the circuit/connections test normal, replace the ECM.
Install a 3-amp fused jumper wire between the signal circuit and the low reference circuit of the HO2S and verify the appropriate HO2S parameter is less than 60 mV.
- If greater than 60 mV, test the signal circuit of the HO2S for an open/high resistance. If the circuit/connections test normal, replace the ECM.
If all circuits/connections test normal, replace the HO2S.