How To Test Automatic Headlight Sensor

How To Test Automatic Headlight Sensor

In this guide on how to test automatic headlight sensor, we discuss what you can do if you’ve been having issues with your sensor. It’s important to address the issues early on to prevent them from affecting your driving experience. 

It is also a good idea to test your car’s automatic headlight sensor before using it while driving. This is because a malfunctioning headlight sensor could cause the headlights to stay on even in daylight. 

Alternatively, it could cause the headlights to turn off unexpectedly when you’re driving at night, or prevent them from turning on altogether. 

We’ve been testing and working on headlights for over a decade. So if you need help figuring out how to test your headlight sensors, allow us to help. 

Keep reading for more information on how to test an automatic headlight sensor. 

What Does An Automatic Headlight Sensor Do?

Automatic headlight sensors are photo-sensitive sensors on your car or other vehicle that detect the absence of light and automatically turn the headlights on at night. 

This is done so that you don’t have to turn the headlights on or off every time you go for a drive. 

Another major benefit of automatic headlight sensors is that they automatically turn the headlights off when you turn off the engine. So even if you forget to turn the headlights off, the sensor prevents them from running and draining the battery. 

Signs Your Automatic Headlight Sensor Is Faulty 

There are a couple of different risks associated with driving a car that has a faulty automatic headlight sensor. 

Battery Drain

One of the biggest (and most common) problems associated with a faulty headlight sensor is battery drain. If your headlight sensor is malfunctioning and causes the headlights to turn on randomly, you might not catch it for a long time. 

This might mean the headlights stay on for a couple of hours at a time. And if that happens when the engine isn’t running, the battery will drain pretty quickly. So the next time you want to drive to work, the engine may not even start. 

Headlights Go Out Unexpectedly

Another even more concerning problem with a malfunctioning automatic headlight sensor is that it could cause the headlights to go out when you’re least expecting it. 

Imagine driving on the highway at night, doing 70 mph, and all of a sudden, your headlights just go out. That’s a major safety concern and one that jeopardizes your and your passengers’ lives. 

Reduced Longevity

And lastly, you might experience reduced longevity of the headlight bulbs if the automatic headlight sensor is malfunctioning. 

If the headlight sensor keeps turning the headlights on in the daytime, it will reduce the lifespan of the headlights for nighttime driving. That means more frequent headlight bulb replacements, and even less effective lighting for nighttime driving. 

How To Test An Automatic Headlight Sensor

So now that we’ve established that a faulty headlight sensor is bad news, let’s discuss how you can test yours and see if it is working properly. 

Step 1: Switch Off Your Headlights

The whole point of an automatic headlight sensor is that you shouldn’t have to give any input for the headlights to start working. So to begin the test, ensure that the headlight switch in your car is turned off. 

Some vehicles with automatic headlight sensors will turn the headlights on in the dark by default. 

On other models, you will have the option to use the headlight sensor or not. This will usually be controlled via the headlight stalk, though you might have to go into the infotainment settings for some vehicles. 

If your car let’s you choose whether or not to use the automatic headlight sensor, make sure it’s enabled, but the manual headlight control switch is turned off.

Step 2: Run The Engine In A Dark Setting

With the headlight switch set to ‘off’ and the automatic headlight sensor-enabled, turn the engine on in a dark setting. This could be in a dimly lit garage or outside at night. 

The automatic headlight sensor is meant to turn the headlights on when the engine is running and the car is in a dark setting. If the headlights turn on, that means the sensor is working as it should. If not, it could mean there is something wrong with it. 

Here, we recommend turning off any bright interior lights in the car. The actual light sensor in most vehicles is mounted in the dashboard. It is possible that even though it is dark outside, the sensor is getting light from a dome light, vanity light, or even the phone flashlight you might be using! 

Step 3: Run The Engine In A Well-Lit Setting

Next, perform the same test in a well-lit area, making sure not to change any of the headlight sensor settings. We recommend doing this outside in direct sunlight, since the lights in your garage might not be bright enough for the sensor to register. 

If the headlights stay off, the automatic headlight sensor is probably working properly. However, if the headlights come on in direct sunlight, there may be something wrong with the headlight sensor. 

How To Fix A Faulty Headlight Sensor

If you’ve determined that the headlight sensor is in fact at fault, there are some things you can try to address it. 

Check The Wiring

It’s possible that the problem isn’t with the sensor itself but with the electrical wiring it uses. This could be in the form of frayed wires, bad conductors, or old wiring that needs to be replaced. 

Check The Car’s Electrical System

It might also be a good idea to do a comprehensive checkup of your car’s electrical system. This should include a thorough inspection of the battery, the alternator, and the wiring leading to the headlights. 

Replace Any Blown Fuses

Another common cause for problems like faulty automatic headlight sensors is a blown fuse. Check your car’s fuse box and see if any of the fuses are blown. These will need to be replaced with the correct size and type of fuse, which you can find by referring to the owner’s manual. 

Replace The Sensor

If all else fails, it is possible that the sensor itself is broken or experiencing issues. If so, your only option might be to replace the sensor itself. 

To do so, you will have to find the right part number, via the owner’s manual or your car manufacturer’s website, order it and install it. Alternatively, you can take your car into the dealer and have them replace the sensor. This is the best course of action, especially if your car is under warranty.


So to sum up, there are a lot of risks associated with a faulty automatic headlight sensor. Some of these are just minor annoyances like a drained battery, while others could be legitimate safety concerns for you and your passengers. 

So if you suspect your car’s automatic headlight sensor is giving you problems, it is important to test it and address the issues early on. 

There are a couple of reasons for faulty headlight sensors, from simple ones like a blown fuse to more serious ones like an issue in the car’s electrical system. 

Whatever the case, it is essential that you find it and fix it for a safer, more convenient driving experience.  

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Hi, I'm Graeme, the author and owner of Before I started this hobby site, I used to work alongside my 'Pops', helping out as he worked as a mechanic for over 50 years. Twenty-five of those he was running his own Auto Electrician & Body Shop, where I fell in love with vehicle lighting. I've taken all our experience online (that's not his gig)… so it’s safe to say there are very few people on the internet who can match our expertise and deep understanding of vehicle mechanics, repairs, parts, and especially headlights. If you've got a bulb question, contact me here, and read more about me and here.