What it means
O2 sensor at bank 2 sensor 3 reports a rich reading suspiciously stable for too long. Sensor 3 is typically downstream of the second catalyst on systems with three-stage aftertreatment; sensor coated with carbon or fuel residue is the typical cause.
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, typically after additional catalyst stages on systems that use it. This code sets when its signal remains rich instead of responding as expected; carbon or fuel residue can leave the sensor unable to track exhaust changes.
Common causes
Most likely first.
- Oxygen sensor coated with carbon or fuel residue
- Oxygen sensor aged or failed
- Signal circuit shorted to voltage
- Engine running rich from a fuel-system or ignition fault
Symptoms
- Check engine light on
- Increased fuel consumption
- Possible rough idle or hesitation
- Failed emissions test
How to diagnose it
- Use freeze-frame and live data to confirm the bank 2 Sensor 3 signal stays rich and compare it with other oxygen sensors.
- Inspect the sensor and nearby exhaust for carbon or fuel residue, and check the sensor bung and joints for leaks.
- Look over the bank 2 Sensor 3 connector and harness for a signal wire short to voltage, heat damage, corrosion, or loose pins.
- Review fuel trims and ignition or fuel-system codes to establish whether the exhaust is genuinely rich.
- Test the signal and heater circuits to the manufacturer's specifications and replace the sensor if it remains rich-biased after wiring and mixture faults are excluded.
Common fixes
- Repair a shorted or heat-damaged bank 2 Sensor 3 signal wire.
- Correct the engine or fuel-system fault causing a real rich mixture.
- Repair an exhaust leak near the third sensor.
- Replace the sensor if carbon or fuel contamination has impaired its response.
Can I keep driving?
A steady light with normal drivability usually allows a short trip, but arrange diagnosis promptly because rich exhaust can raise fuel use and harm the catalyst. Stop driving if the light flashes or the engine runs roughly.
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.