O2 Sensor Circuit High Voltage (Bank 1 Sensor 1)

Possible causes

• CommonGenuinely rich mixture - leaking injector, high fuel pressure
• CommonSensor signal wire shorted to a power supply
• PossibleFailed oxygen sensor
• PossibleSensor contaminated by oil or coolant burning in the engine

What you might notice

• Check engine light on
• Black smoke or fuel smell from the exhaust
• Poor fuel economy
• Fouled spark plugs

What to check, in order

1. Check the fuel trim values. Strongly negative trim confirms the mixture really is rich and the sensor is reporting honestly.
2. Look for signs the engine is burning oil or coolant - either will contaminate the sensor and cause this reading.
3. Inspect the sensor wiring for damage that could short the signal wire to power.
4. Check fuel pressure against specification - high pressure produces a rich mixture across the bank.
5. Inspect spark plugs. Uniform sooting supports a genuine rich condition rather than a failed sensor.