What it means
O2 sensor at bank 2 sensor 3 reports a lean reading suspiciously stable for too long. Sensor 3 is typically downstream of the second catalyst on systems with three-stage aftertreatment.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
Bank 2 Sensor 3 is the third-position oxygen sensor on bank 2, commonly located after additional catalyst stages where fitted. The control module sets this code when its signal stays lean or responds too slowly to changing exhaust conditions.
Common causes
Most likely first.
- Oxygen sensor aged or failed
- Exhaust leak near the sensor
- Signal or heater circuit fault
- Engine running lean from an intake or fuel-system fault
Symptoms
- Check engine light on
- Increased fuel consumption
- Possible rough idle or hesitation
- Failed emissions test
How to diagnose it
- Review freeze-frame data and live readings for bank 2 Sensor 3, comparing its changes with the other sensors during warm operation.
- Inspect exhaust joints and the sensor bung at the bank 2 third-sensor location for leaks that could skew its reading.
- Check the sensor connector and harness for chafing, heat damage, corrosion, or a loose connection, and inspect the heater circuit.
- Check fuel trims and related intake or fuel codes to see whether the engine is actually running lean.
- Test the bank 2 Sensor 3 signal and heater circuits to the manufacturer's specifications and replace the sensor only if the wiring and mixture check out.
Common fixes
- Seal an exhaust leak near bank 2 Sensor 3.
- Repair damaged wiring, connector pins, or the heater circuit.
- Fix an intake or fuel-system fault if it is causing a lean mixture.
- Replace bank 2 Sensor 3 if its response remains slow or lean-biased after circuit checks.
Can I keep driving?
If the warning light is steady and the vehicle runs normally, you can usually drive a short distance, but emissions may be affected and diagnosis should not be put off. Stop if the light flashes or the engine develops a misfire or significant power loss.
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.