Emissions

P01F4 — O2 Sensor Slow Response, Bank 1 Sensor 4

Severity: low Safe to drive

What P01F4 means

The engine control module monitors the oxygen sensor labeled Bank 1 Sensor 4 and found that its signal changes more slowly than expected. An oxygen sensor measures leftover oxygen in the exhaust, which the ECM uses to judge mixture or exhaust treatment performance. Where sensor 4 sits depends on the vehicle's exhaust layout, so confirm its location in the service information for your model.

Symptoms

  • Check Engine light on
  • Increased fuel consumption
  • Rough or unstable idle, or hesitation
  • Failed emissions test
  • Sometimes no symptoms other than the code

Possible causes

  1. Aged or contaminated oxygen sensor (Bank 1 Sensor 4)
  2. Damaged wiring or a corroded connector at the sensor
  3. Exhaust leak near or ahead of the sensor
  4. Sensor heater circuit fault
  5. Mixture problem upstream (injectors, vacuum leak, fuel pressure)
  6. ECM fault (uncommon)

How to diagnose

  1. Scan all codes and freeze frame data, and note any mixture, misfire or catalyst codes
  2. Find Bank 1 Sensor 4 on your vehicle using the service information
  3. Inspect the sensor harness and connector for chafing, heat damage, corrosion or moisture
  4. Look for exhaust leaks at and ahead of the sensor
  5. Watch live sensor data and heater status with a scan tool and compare with the other O2 sensors
  6. Review short and long term fuel trims for upstream mixture faults
  7. Test heater power, ground and resistance against the manufacturer's specs
  8. If wiring and exhaust are fine, replace the sensor and clear the code

Common fixes

  • Replace the Bank 1 Sensor 4 oxygen sensor
  • Repair or replace damaged wiring or connectors
  • Fix any exhaust leak
  • Correct the upstream mixture problem (vacuum leak, airflow sensor, injectors)

Questions and answers

What does P01F4 mean?

It means the Bank 1 Sensor 4 oxygen sensor circuit is responding too slowly. The ECM sees the signal react sluggishly to changes in the exhaust.

Can I drive with code P01F4?

Usually yes for a short time. It is best to fix it soon to avoid wasted fuel and a failed emissions inspection.

Do I always need a new sensor for P01F4?

No. Check the wiring, connector, exhaust leaks and fuel trims first. Replace the sensor if everything else checks out.

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.