P01F2
O2 Sensor Circuit Low Voltage 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
- F2
- FaultThe specific fault in that area
What it means
P01F2 means the engine control unit saw the signal voltage from the Bank 1 Sensor 4 oxygen sensor circuit stay lower than expected. Bank 1 is the side with cylinder one. Sensor 4 is an extra oxygen sensor further along the exhaust, and its position depends on the model and engine. The fault is set when the signal circuit voltage is below the expected range for longer than the control unit allows.
Symptoms
- Engine warning light on
- Usually no obvious change in driving
- Possible slight rise in fuel consumption on some models
- Other oxygen sensor or catalyst monitor codes stored alongside it
- Failed emissions test or readiness monitors not completing
Possible causes
- Faulty or aged Bank 1 Sensor 4 oxygen sensor giving a persistently low signallikely
- Damaged, chafed or heat-melted sensor wiring shorting the signal wire to groundlikely
- Corroded, loose or contaminated sensor connector terminalspossible
- Exhaust leak near the sensor letting in air and skewing readingspossible
- Sensor contaminated by oil, coolant, fuel additives or siliconepossible
- Fault in the control unit sensor input circuitrare
How to diagnose
- Read all stored codes and freeze frame data, and note whether other oxygen sensor, catalyst or fuel trim codes are present.
- Confirm which sensor is Bank 1 Sensor 4 on this engine using the manufacturer's exhaust layout, as this varies by model.
- Inspect the sensor wiring and connector for chafing, heat damage, water ingress and corrosion, and check the routing is clear of the exhaust and moving parts.
- Check the exhaust for leaks or damage upstream of and around the sensor.
- Watch live data for the sensor signal with the engine warm, and see whether it stays stuck low or responds to throttle changes.
- With the connector disconnected and ignition off, check the signal and ground wires for continuity and for shorts to ground against the wiring diagram.
- Check the sensor supply and reference voltages at the connector as specified for that model.
- Check for contamination signs on the sensor and look for engine faults such as oil or coolant consumption.
How to fix
- Replace the Bank 1 Sensor 4 oxygen sensor if it is faulty or contaminated.
- Repair or replace damaged wiring, correcting any short to ground.
- Clean or repair connector terminals, or replace the connector if corroded or loose.
- Repair exhaust leaks near the sensor.
- Fix the source of any contamination, such as oil or coolant entering the exhaust, before fitting a new sensor.
- If all wiring and the sensor test good, have the control unit input checked and repaired as the manufacturer advises.
Can I keep driving?
Low severity
The car can normally be driven while you book it in, as this fault rarely affects drivability. Get it checked soon, since it may stop the emissions monitors completing and could mask other problems.
Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.