Emissions

P01F1 — O2 Sensor Circuit Fault, Bank 1 Sensor 4

Severity: low Safe to drive

What P01F1 means

P01F1 relates to the oxygen sensor circuit for Bank 1, Sensor 4. The engine control module (ECM) compares the sensor's signal with what it expects and sets the code when the signal is missing, unstable or out of range. The exact sensor location and code definition can vary by manufacturer, and the code is reserved in the SAE standard, so confirm it against model-specific data.

Symptoms

  • Check Engine light on
  • Higher fuel consumption
  • Unstable idle
  • Hesitation or rough running
  • Failed emissions test

Possible causes

  1. Failed or aged oxygen sensor (Bank 1 Sensor 4)
  2. Damaged wiring harness or poor connector contact at the sensor
  3. Sensor heater circuit fault
  4. Sensor contaminated by deposits
  5. Exhaust leak near the sensor
  6. Air-fuel mixture problem upstream of the sensor
  7. ECM fault (rare)

How to diagnose

  1. Read all codes and freeze frame data, and look for related mixture or misfire codes
  2. Identify which sensor is Bank 1 Sensor 4 on your specific model
  3. Inspect the sensor wiring and connector for chafing, melting, corrosion or moisture
  4. Test the heater circuit, power supply and ground with a multimeter following the factory wiring diagram
  5. View live sensor data (voltage or current, heater status) on a scan tool
  6. Check the exhaust system for leaks near the sensor
  7. Review short and long term fuel trims for mixture problems
  8. Clear the code after repair and confirm it does not return

Common fixes

  • Replace the Bank 1 Sensor 4 oxygen sensor
  • Repair or replace damaged wiring and connectors
  • Fix exhaust leaks near the sensor
  • Correct any upstream mixture problem found
  • Update ECM software or replace the ECM (only after everything else is ruled out)

Questions and answers

What does P01F1 mean?

It indicates a circuit fault in the oxygen sensor for Bank 1, Sensor 4. Some manufacturers define it differently, so check the documentation for your model.

Can I drive with P01F1?

Usually yes, for short trips. Fuel economy and emissions may suffer and the catalytic converter may be stressed, so get it diagnosed soon.

Is replacing the sensor enough?

Not always. Check the wiring, connector, heater circuit and exhaust leaks first, since the sensor itself is often not the cause.

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.