P00F4: Humidity Sensor Circuit Low
What to do
Ask whether other intake sensor faults are stored at the same time. This sensor usually shares an assembly and a connector with the intake air temperature and airflow sensors, so one wiring fault sets several codes that all clear with a single repair.
Ask for the connector to be checked for water. It sits in the intake where rain and engine bay washing reach it, and that is a common cause.
Mention if the fault comes and goes with the weather — appearing in the wet and clearing when dry points firmly at water in a connector.
Expect no noticeable change in how the car drives, since the engine simply falls back to conservative assumptions.
What this code means
The humidity sensor's signal is below the lowest voltage the circuit should produce.
A signal below the valid range is an electrical statement rather than a claim about the weather. These sensors are specified so their output never reaches either supply rail in normal use — even in completely dry air the signal keeps a comfortable margin above zero. That margin exists precisely so the module can tell a broken circuit from an extreme reading.
So this is a wiring fault until proven otherwise, and the candidates are the usual three: a short to ground, an open signal wire, or a collapsed reference supply.
The shared supply deserves checking early. This sensor typically sits in the same assembly as the intake air temperature and mass airflow sensors and shares their connector and reference — so a single fault there sets several codes that look unrelated. Read the whole stored list before starting; fixing the supply clears them together.
Unplugging the assembly separates harness from sensor in a minute. A circuit that stays low with it disconnected is a wiring or module fault, not a sensor.
Water is the location-specific cause. The intake assembly sits behind the grille where rain and washing reach it, and a connector that has filled reads low, dries out, and returns — which is exactly the intermittent, weather-linked history these often have.
Likely causes
Start here
- Wiring shorted to ground · moderate
- Water ingress into connector · easy
- Corroded or loose connector · easy
Less common
- Faulty humidity sensor · easy
- Failed sensor reference voltage supply · specialist
Symptoms
Components involved
Information, not instruction
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Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
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