O2 Sensor Heater Circuit Malfunction (Bank 1, Sensor 1)
Common Symptoms
- Check engine light on
- Possible rich/lean condition until sensor warms up
- Slightly reduced fuel economy when cold
Most Likely Root Causes
- Failed O2 sensor heater element
- Open or short in heater circuit wiring
- Blown fuse for O2 sensor heater
- Faulty PCM heater control
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Severity / Derate Risk
Low — heater failure causes slow warm-up, not complete sensor failure.
Component Location
Bank 1 Sensor 1 (upstream) — in exhaust manifold or downpipe before catalytic converter, Bank 1 side (cylinder #1 side).
Manufacturer Notes
Heater allows sensor to reach operating temperature quickly. Failure causes open-loop operation longer on cold starts. Check fuse before replacing sensor.
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