Fuel and air

P00F5 — Humidity Sensor Circuit High

Severity: low Safe to drive

What P00F5 means

The engine control unit monitors a humidity sensor, often built into the mass airflow (MAF) sensor or mounted in the intake tract. P00F5 sets when the signal voltage stays above the expected range. This can come from a failed sensor, an open circuit or a short to voltage in the wiring. Humidity data helps the ECU fine-tune fuel mixture and ignition timing.

Symptoms

  • Check Engine light on
  • Erratic or unrealistic humidity readings
  • Slightly reduced performance or higher fuel use
  • Rough idle (uncommon)
  • Climate control oddities on cars with a cabin humidity sensor

Possible causes

  1. Failed humidity sensor or the humidity element inside the MAF sensor
  2. Poor contact in the sensor connector
  3. Open circuit or short to voltage in the wiring harness
  4. Corrosion or moisture in the connector or wires
  5. Faulty ECU or climate control module (rare)

How to diagnose

  1. Read all codes and freeze frame data and record them before clearing
  2. Inspect the sensor connector and harness for moisture, corrosion and chafed insulation
  3. Watch live data: humidity value and signal voltage across different conditions
  4. Unplug the connector and check reference voltage and ground against the wiring diagram
  5. Test the signal wire for a short to voltage and for an open circuit
  6. If wiring is good, swap in a known-good sensor or MAF and compare readings
  7. Clear the code and road test to confirm it does not return

Common fixes

  • Replace the humidity sensor or the MAF assembly
  • Repair the wiring harness or replace the connector
  • Clean the terminals and apply dielectric protection
  • Reflash or replace the ECU if confirmed faulty

Questions and answers

Can I drive with a P00F5 code?

Usually yes. The ECU falls back to a default humidity value, so the car runs normally. Get it checked soon anyway.

What most often causes P00F5?

Most often it is the humidity sensor itself or a MAF sensor with a built-in humidity element, or a corroded connector or damaged wire. ECU failure is very rare.

How do I clear P00F5?

A scan tool can clear it, but it will return until the cause is fixed. Check the sensor and wiring first.

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.