What it means
The downstream oxygen sensor on bank 1 reports a constant rich signal during a forced-lean command. Suggests a failed downstream sensor or a sensor contaminated by oil/coolant from upstream engine wear.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
Bank 1 Sensor 2 measures oxygen in the exhaust after the catalytic converter on bank 1. This code sets when the control module commands a lean condition but the downstream sensor continues to report rich, suggesting a stuck or contaminated sensor or a signal problem.
Common causes
Most likely first.
- Downstream sensor failed stuck rich
- Downstream sensor contaminated
Symptoms
- Check engine light on
- Increased fuel consumption
- Possible rough idle or hesitation
- Failed emissions test
How to diagnose it
- Review freeze-frame and live data for bank 1 Sensor 2 during the reported lean command, and check for related misfire, fuel-trim, or oil-consumption codes.
- Inspect the sensor tip and nearby exhaust for contamination, damage, or leaks, and check whether the engine is consuming oil or coolant.
- Inspect bank 1 Sensor 2 wiring and connector for shorts, corrosion, heat damage, or loose terminals that could hold the signal rich.
- Check the sensor heater and signal circuit, then compare its response with the upstream sensor using the manufacturer's test procedure.
- If the circuit is sound, test whether bank 1 Sensor 2 changes as expected during a controlled lean condition before replacing it.
Common fixes
- Repair a shorted or damaged signal wire or connector at bank 1 Sensor 2.
- Replace bank 1 Sensor 2 if it stays rich during the manufacturer's response test.
- Correct an oil or coolant leak causing sensor contamination.
- Repair an engine mixture or misfire fault indicated by related codes.
Can I keep driving?
Gentle driving is usually possible if the engine runs smoothly, but avoid prolonged trips if fuel consumption rises or the engine hesitates. Continued operation with a genuinely rich mixture can increase emissions and may damage the catalytic converter.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.