What it means
O2 Sensor Signal Biased/Stuck Rich (Bank 1 Sensor 3): the control module has detected this fault condition.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
Bank 1 Sensor 3 is a downstream oxygen sensor fitted on some exhaust systems with a third sensor position. This code sets when its signal remains rich or fails to respond as expected; a contaminated sensor, signal wire shorted to voltage, or a truly rich exhaust condition can produce that result.
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
- Check freeze-frame data and bank 1 Sensor 3 live data, then compare its response with other oxygen sensors to confirm the rich bias is localized.
- Inspect the sensor tip and nearby exhaust for carbon or fuel residue, and check for exhaust leaks around the sensor bung.
- Examine the bank 1 Sensor 3 connector and harness for shorts to voltage, melted insulation, corrosion, or incorrect routing.
- Check fuel trims and ignition or fuel-system codes for evidence that the engine is actually running rich.
- Test the sensor signal and heater circuits against the manufacturer's specifications, then replace the sensor if the circuit and mixture are sound but its signal stays rich.
Common fixes
- Repair a shorted or heat-damaged bank 1 Sensor 3 signal wire.
- Correct the fuel or ignition fault causing a genuinely rich mixture.
- Repair an exhaust leak near the sensor.
- Replace the sensor if carbon or fuel contamination or age has left it unresponsive.
Can I keep driving?
If the light is steady and the vehicle drives normally, limit driving and arrange a prompt check because a real rich-running fault can increase fuel use and damage the catalyst. Stop if the light flashes or the engine misfires.
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.