P01F6
O2 Sensor Signal Biased/Stuck Lean Bank 1 Sensor 4.
- Generic
- Powertrain
- Generic code
- Low severity
How this code is built
- P
- SystemPowertrain
- 0
- Defined bySAE, the same on every car
- 1
- AreaFuel and air metering
- F6
- FaultThe specific fault in that area
What it means
P01F6 means the engine control unit has judged that the signal from the fourth oxygen sensor on bank 1 is biased or stuck at a lean reading (low voltage or high oxygen indication). Sensor 4 is normally a further downstream sensor in the exhaust, and its position depends on the model and exhaust layout. The fault is set when the signal stays lean and does not respond as expected to changes in engine operation or to the other sensors.
Symptoms
- Engine warning light on
- Usually no obvious change in how the car drives
- Possible slight change in fuel economy if the fault is linked to a real mixture problem
- Other fuel trim or oxygen sensor codes stored alongside it
- Failed emissions test or readiness monitors not completing
Possible causes
- Faulty or aged oxygen sensor (sensor 4, bank 1) giving a stuck or biased lean signallikely
- Exhaust leak near the sensor letting outside air in and giving a false lean readinglikely
- Damaged wiring, poor connector contact, corrosion or a short or open circuit in the sensor signal or reference wirespossible
- Sensor contamination from coolant, oil, silicone or fuel additivespossible
- A genuine lean condition upstream, such as an air leak, low fuel pressure or a fuel delivery faultpossible
- Catalytic converter fault that affects the downstream oxygen readingrare
- Engine control unit fault or outdated softwarerare
How to diagnose
- Read all stored and pending codes and note the freeze frame data, including load, engine temperature and fuel trims, then check for related fuel trim, misfire or other oxygen sensor codes.
- Use the manufacturer's information to confirm exactly where sensor 4 on bank 1 is fitted on this model and engine.
- Visually inspect the sensor wiring, routing and connector for heat damage, chafing, corrosion, water ingress or a loose fit.
- Inspect the exhaust from the manifold to the sensor for leaks, cracked joints, failed gaskets or damaged flexible sections.
- Check live data for short and long term fuel trims on bank 1 to see whether the engine is genuinely running lean, and rule out air leaks and fuel delivery problems.
- Watch the sensor 4 live signal and compare it with the other bank 1 sensors; see whether it stays stuck lean or reacts to throttle changes and fuel cut on overrun.
- Check the sensor's supply, heater and signal circuits for correct voltage, continuity and resistance against the manufacturer's specification.
- Look for technical bulletins or software updates relating to this code for the vehicle before replacing parts.
How to fix
- Repair or replace damaged wiring or connectors in the sensor circuit.
- Repair exhaust leaks and replace failed gaskets or damaged pipe sections.
- Replace the oxygen sensor if it is confirmed faulty or contaminated, and fix the source of any contamination first.
- Correct any underlying lean condition, such as vacuum or intake leaks or fuel delivery faults.
- Replace the catalytic converter only if testing shows it has failed and is the root cause.
- Apply an updated control unit software calibration if the manufacturer lists it as a fix for this code on the vehicle.
Can I keep driving?
Low severity
The car can normally be driven while you book it in for diagnosis. If the engine runs roughly, hesitates or shows other warning lights, get it checked sooner.
Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.