Car Headlights Won't Turn Off

headlights won't turn off
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Question: Why won’t my car’s headlights turn off?

I’m having this problem where my car headlights won’t turn off. It doesn’t matter if I turn them off manually or not. When the engine is shut off and the keys are removed, the headlights just stay on and they never go off. This is going to kill my battery, right? But I don’t know what to do.

Answer:

Headlights aren’t the most complicated tech, even in newer cars with fancy systems like adaptive headlights, but there are a handful of different points of failure that could result in the situation that you’re describing.

You may be able to track down and fix the problem yourself with the right diagnostic tools, or you may end up having to take the car to a professional.

In the meantime, there are also a couple ways to prevent your battery from dying in the short term if you can't get your headlights to turn off right away.

Quick Fix to Prevent Your Headlights From Draining the Battery

If you don’t have time to tackle the problem right away, or you just want to be able to leave the car for a while without the battery dying, there are two different ways to keep the headlights from killing the battery.

The easiest way to keep the battery from dying is to straight up disconnect it. If you’ve never done that before, then you’ll just want to make sure that you disconnect the negative cable (typically black) instead of the positive cable (typically red) to avoid even the possibility of a short circuit. Once the battery is disconnected, the headlights will turn off, and the battery won’t die.

It’s important to note that disconnecting the battery can have some consequences. The memory of your computer will be wiped out, so it will have to go through a “relearning” process that may impact fuel economy for a short time. You also won’t be able to go through emissions testing in places where they read the codes as part of the test since it will show that the battery was disconnected.

If your car stereo has a security feature that requires a special code after a loss of power, then you’ll also want to make sure you find your car radio code before you disconnect the battery.

The other way to shut the headlights off is to remove the appropriate fuse or relay. This is a little more complicated than disconnecting the battery since you will have to locate the correct fuse panel and then figure out which fuse or relay to pull. It will prevent a loss of power to the computer and radio, though, so you won’t have to deal with any fallout later on.

What Can Cause Headlights to Stay On?

Some of the issues that can cause car headlights not to turn off include problems with a:

  • Headlight switch
  • Multifunction switch
  • Daytime running light module
  • Light sensor
  • Relay

The matter of actually tracking down the problem can be complicated since there are so many different types of headlight systems out there. For instance, some cars are designed so that if the engine is shut off while the headlights are on, they will remain on for a specific amount of time. If you have one of those cars, that system may have failed, and you might want to try shutting the headlights off before turning the engine off and removing the keys to see if that helps.

Other cars have daytime running lights, which is essentially just a system that automatically turns the headlights on—but doesn’t affect the dash lights—during the day. If that system fails, it may cause the headlights to remain on. In that case, you can try setting the parking brake to see if that shuts the headlights off, as setting the parking brake typically disables daytime running lights. If that’s the case for you, then removing or replacing the daytime running light module will probably fix your problem.

If a bad headlight relay is a reason that your headlights won't turn off, then the fix there is also to just replace the relay.

This is actually a little easier to check yourself, some many situations, since there's a chance that multiple circuits may use the exact same type of relay. If this is the case, then you can actually just remove your headlight relay, swap it for an identical one from a different circuit, and see if your headlights turn off normally.

In the event that your problem is a bad headlight switch, multifunction switch, or light sensor, the diagnostic procedure will be more complex. You may be able to identify the problem by simply removing the component in question and checking for physical damage, but there won't always bee physical indicators. For instance, a bad headlight switch that's shorted internally may get hot enough to crack, melt, or even burn the plastic housing or electrical connections, but that isn't always the case.

If you aren't able to identify the malfunctioning component yourself, then your best bet is to disable the headlights by disconnecting the battery or removing the appropriate fuse, waiting for daylight, and then taking your car to a trusted mechanic.