Emissions

P01F6 — O2 Sensor Signal Biased/Stuck Lean (Bank 1 Sensor 4)

Severity: medium Safe to drive

What P01F6 means

Oxygen sensors measure how much oxygen is left in the exhaust, and the engine control unit uses that data to judge catalyst performance and mixture quality. P01F6 sets when the signal from Bank 1 Sensor 4 stays lean or is shifted away from the expected range. Sensor numbering varies by manufacturer, and sensor 4 usually sits further along the exhaust than the standard downstream sensor. Check the wiring diagram for your model to locate it.

Symptoms

  • Check Engine light on
  • Possibly higher fuel consumption
  • Unstable idle (if there is a real lean condition)
  • Sluggish acceleration (not always)
  • Often no symptoms other than the code

Possible causes

  1. Failed or aged Bank 1 Sensor 4 oxygen sensor
  2. Damaged wiring or poor connection at the sensor connector
  3. Exhaust leak upstream of or near the sensor
  4. Sensor heater circuit fault
  5. Sensor contamination (oil, coolant, deposits)
  6. A real lean mixture from a vacuum leak or fuel delivery problem

How to diagnose

  1. Scan all codes and freeze frame data, and look for mixture codes such as P0171.
  2. Use the wiring diagram to confirm which sensor is Bank 1 Sensor 4 on your vehicle.
  3. Inspect the sensor, harness and connector for melting, corrosion or chafed insulation.
  4. Check the exhaust for leaks upstream of and around the sensor.
  5. View live sensor voltage or current and heater status on a scan tool, and compare with the other sensors.
  6. Check short and long term fuel trims; a large positive value points to a vacuum leak or fuel supply problem.
  7. Test the sensor's power, ground and heater resistance with a multimeter.
  8. Clear the code and road test to confirm it does not return.

Common fixes

  • Replace the Bank 1 Sensor 4 oxygen sensor
  • Repair the wiring or replace the connector
  • Fix the exhaust leak ahead of the sensor
  • Repair the vacuum leak or fuel delivery fault if fuel trims show a lean condition

Questions and answers

Can I drive with a P01F6 code?

Usually yes, if the car runs normally. Still, get it checked soon, because a true lean condition can cause misfires and strain the catalytic converter.

Should I replace the oxygen sensor right away?

No. First check the wiring, connector, exhaust leaks and fuel trims. Replace the sensor once those are ruled out or its readings are clearly wrong.

What does Bank 1 Sensor 4 mean?

It is the fourth numbered oxygen sensor on the side of the engine that has cylinder 1. Its exact position depends on the exhaust layout, so check the diagram for your model.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.