O2 Sensor Circuit High Voltage (Bank 1, Sensor 2)

Common Symptoms

• Check Engine Light on
• Engine runs rich downstream
• Catalyst overheating risk
• Poor fuel economy

Probable Causes (Ranked by Likelihood)

• O2 sensor stuck in rich/high state Very High
• Genuine rich exhaust condition after catalyst Moderate
• Sensor contaminated with coolant or oil causing rich bias Moderate
• Short to voltage on signal wire Low

Step-by-Step Diagnostic Procedure

1. Monitor downstream O2 voltage. Should be relatively stable at 0.6-0.8V in normal operation.

2. If voltage is stuck above 0.9V constantly, suspect sensor contamination or a stuck-rich sensor.

3. Check for coolant burning: sweet smell from exhaust, white smoke on deceleration.

4. Check for oil burning: blue smoke, excessive oil consumption.

5. Replace sensor if contamination is confirmed.

Frequently Asked Questions