P00F4: Humidity Sensor Circuit Low

What it means

The control module monitors the humidity sensor signal. It sets this code when the signal falls below the expected range.

At a glance

• Usually lights the check-engine light
• Affects emissions; the car can fail an emissions test

How it works

The humidity sensor reports moisture information to the control module for related system decisions. This code sets when the sensor signal falls below the expected range, which can result from a signal wire short to ground, damaged insulation, or poor connector contact.

Common causes

Most likely first.

1. Signal wire shorted to ground
2. Connector pins corroded - high contact resistance
3. Harness chafing through insulation

Symptoms

• Check-engine light on
• Automatic climate control may work less accurately
• Windshield may fog more easily

How to diagnose it

1. Save freeze-frame data and check scan-tool readings for a humidity signal that is unusually low or fixed, along with related codes.
2. Inspect the humidity sensor connector for corrosion and check whether the terminals fit securely.
3. Trace the harness for chafing or insulation worn through, especially where it contacts metal edges or moves with vibration.
4. Use the wiring diagram to test the signal circuit for a short to ground and check continuity through the harness.
5. Test the sensor and circuit against the manufacturer's specification to identify whether the low reading comes from the sensor or wiring.

Common fixes

• Repair chafed wiring or a signal wire shorted to ground.
• Clean corroded connector pins and restore proper contact.
• Replace damaged sections of the humidity sensor harness.
• Replace the humidity sensor if it fails testing with a sound circuit.

Can I keep driving?

Driving is generally unaffected, but climate control may handle humidity poorly and the windshield may fog more readily. Keep the glass clear and stop somewhere safe if visibility becomes impaired.