Q: Headlights coming on and draining battery

asked by on January 28, 2016

The headlights in my car are coming on while my car is off, draining the battery. Even if I go out and turn them back off, they come on by themselves again.

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It sounds like there could be a short in the wiring that controls your automatic headlight system. When the automatic light system is selected the vehicle uses a ambient light sensor usually located on the dash to detect how much ambient light there is. If the sensor sees that it is getting dark at a certain point the light will turn on, as well as if there’s enough light they will shut off. This command to turn the light on or off is controlled by the body control module. When the car is shut off and the doors are locked in some cases the lights will stay illuminated for a set amount of time until the body control module shuts off and turns the lights off. If the body control module is malfunctioning the module can stay on and eventually kill the battery. A parasitic draw test should be performed to pinpoint the cause of the unnecessary draw of power.

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