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Car Brake Lights Stuck On Off Cant Start Brake Switch Diagnosis

Created on: 2020-10-12

In this video Len shows you how to diagnose the brake switch and figure out if you need to replace yours, or it just needs an adjustment!

Whoa. Hey, buddy. Where's your brake lights?

Hey, friends, it's Len here from 1A Auto. Have you ever been behind somebody that just seems like they drive around with their brake pedal on the whole time, whether accelerating up a hill, down a hill, around a corner, whatever they're doing, brakes are always on? Or maybe you've been driving behind somebody and they magically seem to step on the brakes or the car stops without actually having any lights on at all? With that said, I kind of want to go over some of the symptoms of what's going on, and I also want to let you know where I would start. If I was diagnosing. Obviously, fixes for brake light issues you'd want to start with the basics. You want to check the fuses, the relays, and, of course, the bulbs. If you find that all those seem as though they're good, the next likely candidate would be at the brake lamp switch.

Now, generally, underneath the driver's side of your dash, along that brake pedal assembly, you're going to find your brake light switch. Now, on most older vehicles, the brake light switch, essentially just did one thing, it kind of turned on those brake lights so people that were behind you knew that you were slowing or stopping. On newer vehicles, some of the other things that the brake light switch might tend to do would be a shift interlock. You know what I'm talking about? Where you're in park, you go to shift into maybe reverse or even drive, of course, you're going to have to step on that brake pedal first. If the vehicle's computer doesn't know you're stepping on the brake, you're not going to be able to shift it.

Other than that, if you have a push-button start on your vehicle, you know you're going to have to push on that brake, push the button to be able to start it. If the vehicle, once again, doesn't know that you're stepping on the brake pedal, it's just going to go into accessory mode and you're going to be like, "Why won't this thing start?" Other than that, like I said before, if the brake lamp switch wasn't functioning the way it should, either your brake lights might not work at all or they might just be on for an extended period of time, even when you're not pressing on that brake pedal. Things to think about when we're talking about a brake light switch might be the fact that it could just be out of adjustment. On a lot of vehicles, they have a little adjustment. And if it's too far adjusted, you might have an issue where maybe your brake lights either stay on or they don't come on when you step on the brake pedal itself.

So, looking under the dash, you can see the brake light switch right here. If I press on the brake pedal, you can see that little piston come down, and that means that the brake lights should be on. If I release it, that's going to turn off the brake lights. If this is adjusted to the point where it's coming out further, what you're probably going to notice is it looks as though the brake lights are just always on. If you have it adjusted in too far, you're going to have to step on the brake quite a bit before it actually relieves that piston right there. In which case, you might be actually stopping pretty fast and the person behind you might not even know it yet.

So, I'm just gonna go ahead and pull this out of here. And at this point, I'm going to test to see if this piston's working. Press in and it springs right back out. As you can tell, there's a lot of gunk on it right there. If it gets gunked up on the inside, this might not be able to function and it might get stuck in this position or even in that position. Either way, that's going to be an issue. Other than that, what you can look for is discoloration on it. If it looks as though it's been overheated in any way, obviously, that's going to be an issue as well. And, of course, it has all the wiring that goes to it. On older vehicles, you might notice there's less wires and on newer vehicles or especially vehicles that are more electronic, you might even notice more wiring. If there's any issues with that, such as corrosion or melted wires, you're going to find an issue as well.

Now, this brake light switch doesn't have an adjustment but assuming it did, and you had it actually into the vehicle, what you would want to make sure is that you have a tiny bit of pressure on that piston so that way there, it didn't just necessarily turn on those brake lights every time you just barely bonk this brake pedal. Obviously, hitting bumps and this doing this down the road, the person behind you is not gonna want to see those brake lights flashing like a maniac. Generally, when you have no pressure on your brake pedal the switch is in the open position, which essentially means that it's not creating an electrical circuit. So, there's no way for your vehicle to know that you're pressing on the brake in exception of the physical pressure you're putting on the hydraulic aspect of your braking system. Essentially, the car's computer doesn't know you're telling it to stop.

Luckily, this doesn't affect the actual breaking of your vehicle, but it can cause other issues, not just with your vehicle, but it could potentially with other people. Obviously, you can imagine if the vehicle in front of you just came to a complete stop right in front of you, a panic stop. But for some reason, their brake lights didn't work, you have a split instant that you have to try to make a decision. Overall, it would be nice to have some brake lights on right in front of your face so you know what's going on. Without those though, you just kind of have to judge the fact that, "Whoa, this vehicle in front of me is coming to a stop." Obviously, this puts you and everybody else in an unsafe predicament.

With that said, if your brake lights aren't functioning properly, well, then you're going to have an issue. Generally, the brake lights should turn on almost instantly after pressing on the brake. With that said, the people behind you need to know when you're pressing on that brake. With that said, go ahead and pull out your brake light switch, give it a quick peek, make sure it doesn't look like it's burnt or cooked in any way. Make sure the electrical connector looks like it's in good condition. And double-check that little piston, make sure it functions as it should. If you squeeze it and it gets stuck in the up position, well, you know that's an issue.

Okay, friends, so that's what I got for you on brake light switches. Hopefully, it helps you out a little bit along the way. If you like the video smash on the light button for me, it would mean the world. Leave me a comment because I always like to hear from you. And, of course, subscribe and ring the bell, that way there, you can be kept up with all of our latest content. Thanks.

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