Symptoms
- Headlights don't turn on automatically at dusk or in tunnels
- Manual headlight operation still works fine
- Switch is confirmed to be in the 'auto' position
- Dash light sensor location looks obstructed or dirty
Likely causes
- CommonDirty or obstructed ambient light sensorThe sensor (often near the top of the dash or windshield) needs a clear view to detect light levels.
- PossibleSensitivity setting adjusted too lowSome vehicles allow adjusting how dark it needs to be before auto headlights activate.
- PossibleFailed light sensorThe sensor itself can fail electronically over time.
- PossibleSwitch not fully in the auto positionThe headlight switch may be slightly off from the true auto setting.
What to do
- Confirm the headlight switch is fully and correctly set to the 'auto' position.
- Locate the ambient light sensor (commonly near the top of the dash or by the rearview mirror) and clean any dust or obstruction.
- Check your vehicle's settings menu (if equipped) for an auto headlight sensitivity adjustment.
- Test manual headlight operation to confirm the bulbs and basic wiring are working fine.
- Try covering the sensor with your hand in daylight to see if headlights activate, confirming the sensor is being read at all.
- Avoid relying solely on auto headlights until the issue is resolved; manually turn on headlights in low light conditions.
- Have a shop test the sensor circuit if cleaning and setting checks don't resolve the issue.
- Replace the sensor if it's confirmed faulty through testing.
Tools and parts
- Clean, soft cloth (for sensor)
Ambient light sensorSearch: “auto headlight sensor for [your car make model year]”
When to call a pro
If your vehicle has an adjustable auto headlight sensitivity setting, check that first, since it's the easiest and quickest thing to overlook.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.