P01F4
O2 Sensor Circuit Slow Response 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
- F4
- FaultThe specific fault in that area
What it means
P01F4 means the engine control unit has judged that the oxygen sensor at Bank 1, Sensor 4 is reacting too slowly to changes in exhaust gas oxygen content. The control unit compares the signal's response with what it expects when fuelling changes or during fuel cut-off, and the sensor lagged beyond the limit. Sensor 4 is only fitted on some exhaust layouts, so its location depends on the model and engine.
Symptoms
- Engine warning light on
- Usually no noticeable change in driving
- Slightly higher fuel consumption in some cases
- Other oxygen sensor or catalyst efficiency codes stored alongside
- Failed emissions test or readiness monitors not completing
Possible causes
- Ageing, contaminated or failing oxygen sensor element giving a sluggish signallikely
- Exhaust leak near the sensor letting in outside air and distorting readingspossible
- Damaged wiring, poor connector contact or corrosion in the sensor circuitpossible
- Sensor heater circuit fault leaving the sensor too cool to respond properlypossible
- Sensor contamination from oil, coolant, silicone or poor-quality fuel additivespossible
- Underlying fuelling or misfire problem upsetting exhaust gas compositionrare
- Control unit fault or outdated software where the manufacturer has documented it as a causerare
How to diagnose
- Read all stored and pending codes and note freeze frame data such as engine temperature, load and speed when the fault set.
- Check the vehicle's exhaust layout and wiring diagram to confirm which sensor is Bank 1 Sensor 4, as this varies by model and engine.
- Inspect the sensor wiring, connector and harness routing for heat damage, chafing, water ingress and corrosion.
- Look and listen for exhaust leaks between the engine and the sensor, including joints, gaskets and flexible sections.
- Check for other related codes, fuel trim problems, misfires, or signs of oil or coolant burning that could contaminate the sensor.
- Watch the sensor's live data on a scan tool graph while holding steady revs and during a throttle snap, checking for slow or lazy switching compared with the other sensors.
- Test the sensor heater circuit for correct resistance, power and earth, following the manufacturer's specification for that sensor.
- Check for a relevant manufacturer service bulletin or software update for this code on your specific model.
How to fix
- Replace the Bank 1 Sensor 4 oxygen sensor if it is slow, contaminated or out of specification.
- Repair any exhaust leak near the sensor and replace faulty gaskets or sections.
- Repair or replace damaged wiring and connectors in the sensor circuit.
- Correct any underlying engine fault such as misfire, rich or lean running, or oil or coolant consumption before fitting a new sensor.
- Apply a manufacturer-issued control unit software update only if a known fault or outdated calibration is documented for the vehicle.
Can I keep driving?
Low severity
The car can normally be driven while you book it in for diagnosis. Fix it reasonably soon, because the cause could be affecting emissions or may point to a problem that gets worse.
Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.