Circuit/System Verification

Allow the engine to reach operating temperature. With the engine running, observe the affected HO2S parameter with a scan tool.
- The HO2S 1 value should vary from below 200 mV to above 800 mV and respond to fueling changes.
- The HO2S 2 value should change more than 200 mV when the throttle is quickly cycled three times from Closed to Wide Open and back to Closed after running the engine at 1500 RPM for 30 seconds.
If any HO2S heater DTCs are set, diagnose those DTCs first.
The affected HO2S may be damaged due to contamination. Prior to replacing the affected HO2S, inspect for the following sources of contamination:
- A silicon contaminated HO2S
- Fuel contamination-Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
- Engine oil consumption-Refer to Oil Consumption Diagnosis .
- Engine coolant consumption-Refer to Loss of Coolant .