Fuel and air

P00F4 — Humidity Sensor Circuit Low Voltage

Severity: low Safe to drive

What P00F4 means

The engine control module monitors the intake air humidity sensor, since humidity changes air density and combustion and is used to fine-tune fuel and spark. P00F4 sets when the sensor signal voltage falls below the expected range. Common reasons are a failed sensor, an open or grounded wire, or a poor connection.

Symptoms

  • Check Engine light on
  • Rough idle
  • Hesitation during acceleration
  • Reduced fuel economy
  • Intermittent performance issues

Possible causes

  1. Failed humidity sensor (often combined with the intake air temperature sensor)
  2. Open circuit or short to ground in the sensor wiring
  3. Corroded or loose connector terminals
  4. Moisture or oil in the connector
  5. Reference voltage or ECM fault (rare)

How to diagnose

  1. Scan all codes and freeze frame data, clear the code and see if it returns
  2. Inspect the sensor connector and harness for moisture, corrosion and chafing
  3. Watch humidity and intake air temperature in live data for unrealistic values
  4. Use a multimeter to test reference voltage, ground and signal wire per the factory diagram
  5. Check the harness to the ECM for opens and shorts to ground
  6. Wiggle the harness and connector with the engine running while watching the data
  7. Replace the sensor if the wiring tests good

Common fixes

  • Replace the humidity sensor or the sensor assembly
  • Repair the wiring and clean or replace the connector
  • Fix any moisture entry and treat the terminals
  • Test and, if needed, repair or reflash the ECM

Questions and answers

What does P00F4 mean?

It means the humidity sensor circuit voltage is too low. The ECM gets a signal below normal and cannot properly account for air humidity.

Can I drive with P00F4?

Usually yes. You may see minor hesitation and higher fuel use, but there is little risk to the engine. Still, get it diagnosed soon.

How do I fix P00F4?

Start by inspecting the sensor connector and wiring, then test the signal with a multimeter. If the wiring is fine, replace the sensor.

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.