Faulty humidity sensor (internal fault or contamination) giving a low signal; Damaged, chafed or corroded wiring causing a short to earth on the signal circuit; Poor connection at the sensor or control unit connector (corrosion, bent or loose pins, water ingress); Open circuit or missing supply voltage or earth to the sensor; Sensor signal shared with a combined sensor (for example an intake air sensor) that has failed; Fault inside the engine control unit.

P00F4

Humidity Sensor Circuit Low.

Generic
Powertrain
Generic code
Low severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
0: AreaFuel and air metering, auxiliary emission controls
F4: FaultThe specific fault in that area

What it means

P00F4 means the engine control unit has seen the signal from a humidity sensor circuit sit lower than the expected voltage range. This usually points to a short to earth, an open or high-resistance fault in the circuit, a missing supply, or a faulty sensor. The sensor's position and how its data is used vary by model and engine, so check the manufacturer's information for the vehicle.

Symptoms

Engine warning light on
Slightly rough running or hesitation in some conditions, depending on how the system uses humidity data
Poor fuel economy or altered performance
Climate or other humidity-dependent functions behaving oddly, if the sensor is shared with other systems
No noticeable symptoms other than the warning light

Possible causes

Faulty humidity sensor (internal fault or contamination) giving a low signallikely
Damaged, chafed or corroded wiring causing a short to earth on the signal circuitlikely
Poor connection at the sensor or control unit connector (corrosion, bent or loose pins, water ingress)likely
Open circuit or missing supply voltage or earth to the sensorpossible
Sensor signal shared with a combined sensor (for example an intake air sensor) that has failedpossible
Fault inside the engine control unitrare

How to diagnose

Read all stored and pending codes and note the freeze frame data, including conditions when the fault set
Check for other related codes, such as intake air temperature or sensor supply voltage faults, which may point to a shared cause
Visually inspect the sensor, its connector and the wiring for damage, chafing, corrosion, moisture or oil contamination
With the ignition on, view live humidity sensor data and compare it with the expected ambient conditions; check whether it is stuck low
Disconnect the sensor and check for the correct supply voltage and a good earth at the connector, using the manufacturer's wiring diagram
Check the signal wire for a short to earth and for continuity and resistance back to the control unit
Wiggle test the harness and connector with live data displayed to find an intermittent fault
If wiring and supply are good, test or substitute the sensor following the manufacturer's procedure before suspecting the control unit

How to fix

Repair or replace damaged wiring, correcting any short to earth or open circuit
Clean, repair or replace corroded or loose connector terminals and ensure the connector is fully seated
Replace the humidity sensor, or the combined sensor assembly if it is supplied that way
Restore the supply or earth to the sensor by repairing the relevant circuit fault
Only if the manufacturer lists a known fault, have the control unit checked and repaired or updated to the approved software

Can I keep driving?

Low severity

The car can normally be driven while you book it in, as the control unit will usually use a default value. If the car starts running poorly or other warning lights appear, have it checked sooner.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.