What it means
A general fault has been detected in the downstream (post-catalyst) oxygen sensor on bank 1. The downstream sensor monitors catalyst efficiency rather than fuel mixture; with no signal, the catalyst monitor cannot run.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The Bank 1 Sensor 2 oxygen sensor sits after the catalytic converter and reports the oxygen level in the exhaust leaving that catalyst. The control module checks its signal and wiring during the catalyst monitor; this code sets when it detects a general fault in that downstream sensor circuit and cannot rely on the reading.
Common causes
Most likely first.
- Downstream sensor aged
- Wiring chafed against exhaust
Symptoms
- Check engine light on
- Failed emissions test
How to diagnose it
- Read the freeze-frame data and monitor status to see when the Bank 1 Sensor 2 fault was recorded and whether the catalyst monitor completed.
- Inspect the downstream sensor, connector, and harness along the exhaust for heat damage, corrosion, loose pins, or chafing.
- Check for exhaust leaks around the sensor and catalyst outlet that could distort the sensor reading.
- With a scan tool, compare Bank 1 Sensor 2 live data with the upstream sensor after the engine is warm and note whether the downstream signal is present and plausible.
- Test the sensor signal and heater circuits for continuity, shorts, and connector faults using the vehicle wiring diagram and manufacturer's specification.
Common fixes
- Repair chafed or heat-damaged wiring to Bank 1 Sensor 2.
- Clean or repair corroded or loose connector terminals.
- Repair an exhaust leak near the downstream sensor.
- Replace the Bank 1 Sensor 2 oxygen sensor if its signal or circuit tests show it has failed.
Can I keep driving?
With no drivability symptoms, short trips are usually possible, but the check-engine light may stay on and the vehicle may fail an emissions test. Arrange diagnosis soon because the catalyst monitor may not be able to assess emissions performance.
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.