Emissions

P01F5 — O2 Sensor Circuit No Activity (Bank 1 Sensor 4)

Severity: low Safe to drive

What P01F5 means

The engine control module monitors the signal from an additional oxygen sensor labeled Bank 1 Sensor 4. This sensor helps evaluate exhaust composition and how the emissions system is working. P01F5 is stored when the signal in that circuit stays flat and shows no sign of activity. Where sensor 4 sits depends on the vehicle's exhaust layout.

Symptoms

  • Check engine light on
  • Worse fuel economy
  • Slightly rough idle (sometimes)
  • Reduced performance (sometimes)
  • Higher emissions, possible inspection failure

Possible causes

  1. Failed or aged Bank 1 Sensor 4 oxygen sensor
  2. Damaged, open or shorted wiring, or corroded connector terminals
  3. Heater circuit fault in the sensor
  4. Exhaust leak near the sensor
  5. Sensor contamination (soot, oil, coolant)
  6. Faulty ECM (rare)

How to diagnose

  1. Scan all codes and freeze frame data, noting any fuel trim or other O2 sensor codes
  2. Find Bank 1 Sensor 4 using the vehicle's service information
  3. Inspect the sensor, harness and connector for chafing, heat damage, moisture and corrosion
  4. Check the exhaust for leaks near the sensor
  5. View live sensor data (voltage or current) and see whether it responds to load changes
  6. Test power, ground and heater resistance with a multimeter against specs
  7. Test the wires between sensor and ECM for opens and shorts
  8. Review fuel trims for a mixture problem upstream

Common fixes

  • Replace the Bank 1 Sensor 4 oxygen sensor
  • Repair the wiring or replace the connector
  • Fix any exhaust leak
  • Correct the cause of contamination (oil burning, coolant leak)
  • Reflash or replace the ECM only after everything else is ruled out

Questions and answers

What does P01F5 mean?

The ECM detected no activity in the Bank 1 Sensor 4 oxygen sensor circuit. The cause may be the sensor, its wiring, the heater, or rarely the control module.

Can I drive with P01F5?

Usually yes for a short time. Fuel economy and emissions may get worse, so have it checked soon.

Will replacing the sensor fix it?

Not always. Check the wiring, connector and exhaust for leaks first, otherwise a new sensor may set the same code.

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.