P01F4O2 Sensor Circuit Slow Response Bank 1 Sensor 4
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- Sensor 4 on bank 1 is a fourth oxygen sensor, behind a third converter or converter brick. The OBD standard provides for up to four sensors per bank, and the code standard defines sensor 4 for bank 1 only. No manufacturer or vehicle using these codes could be identified; the description rests on CARB's requirements for downstream oxygen sensors and the logic of sensors 2 and 3. A switching sensor delivers about 0.1–0.9 V. P01F4 means the sensor reacts too slowly to mixture changes; CARB requires at least a rich-to-lean response test of downstream sensors during fuel cut-off. Behind several converters the oxygen storage buffers the change, so limits are wide.
- What you may notice
- Check engine light on (usually after two drive cycles)
- Catalyst monitor readiness possibly not set
- Usually no change in driving
- Likely causes
- LikelySensor aged or contaminated
- PossibleExhaust leak ahead of the sensor
- PossibleSensor heater weak
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Easy · Often possible to do yourself.Typical cost: €60 – €300
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.