Car brake activating while unoccupied. Wtf.

desperaterobots

So I went to go to the doctor today and do some shopping. Had a flat battery.

Turns out my brake light is activating when I'm not in the car. I leave the car, the brake lights are off. I go outside, my brake lights are on.

Nope, the headlights are all off. It's as though the weight of the brake pedal is enough to depress itself and activate the brake lights. This hasn't happened before. I'm "fixing" it by bending a thong underneath the brake to keep it pushing upwards, like a spring. But has this happened to anyone else, and does anyone know how much it might cost to fix?

I am guessing getting the thing to a mechanic is the obvious thing to do. Just looking for a ballpark figure here, or a suggestion as to what might be causing the issue in the hope I might solve it myself. Any mechanically inclined PA'ers?

RUNN1NGMAN

Low brake fluid pressure? When's the last time you had your brake fluid flushed?

BEAST!

What kind of car do you have that the brake lights work when the car isn't on? There should be no way that those turn on unless the ignition is turned.

If your brake pedal is falling down though I would agree that it's a good chance it's brake fluid pressure.

tsmvengy

Umm, don't brake lights work when the car is off in, like, every car?

It could be brake fluid pressure, but if that were the case I would think your brakes wouldn't be working properly when you drive it. Are they?

Alternatively there could be a wiring issue/short.

flatlinegraphics

if its a vw, there is a switch behind the break pedal that activates the light. the spring wears out, and then it stays active. the replacement is like $20, and is really easy to do, though you end up upside down under the dash swearing at it for a bit.

if its not a vw, i don't know. but it could be something similar.

desperaterobots

Thanks guys. You must be right about brake fluid pressure. I don't remember the last time it was flushed, though it is a little overdue for a service. After I got a jump start I drove around for about 40 mins to recharge the battery some. I noticed the brake light was activating while I was driving around, just by itself. When I got back home I pumped the brake a few times, and as I did, the brake became more and more resistant to pressure.

Sound like a brake fluid thing?

b0bd0d

You could have a short somewhere that's making the brake lights come on. And he's right, there is a switch that turns the brake lights on and off when you press the brake. Crawl under your dash and follow the pedal up and you'll see it. Mine went bad too but opposite from your problem. My brake lights didn't work and I couldn't shit outta park. Is your pedal wobbly or can you grab it and pull it up more? I don't think brake fluid pressure is the problem. It kinda doesn't work like that. And you can light the brake lights up by stepping on the pedal even if the car is off. I think it's the switch. On my car it's call the BOO, brake operated...something. You can try replacing it. Shouldn't be too hard or expensive to do yourself.

...wait, here's a test. next time it does that, without touching anything, try and shift the car outta park. Don't touch the brake or turn the car on or anything. You wanna see if it's caused by the brake switch or something else. See, if the brake switch is going bad or something, the car thinks the brake is pressed. If the brake is pressed, it will allow you to shift outta park. If it's not pressed, meaning the switch isn't pressed, it won't shift outta park.

desperaterobots

The pedal isn't wobbly or loose. It just doesn't resist gravity enough to stop itself from falling the half-inch needed to activate the brake light. But if I pump it enough when the car is turned off, the resistance is fine and the pedal doesn't activate the light.

While driving, the brake lights randomly start shining. I noticed going down a rough street that they were turning on and off as the car went over the bumps. While driving on a main road they were activated the whole time, until i noticed and nudged the pedal back up to 'off'. After a while, it sank back down again.

I'll take a look at the switch and spring stuff under the dash in the mean time, thanks.

Shark_MegaByte

This happened to my '92 Civic. There was a part that's supposed to apply upward pressure against the brake pedal to keep a circuit from closing and turning on the brake light. That part wears out, the circuit will close and the light comes on to drain your battery.

I don't remember how much it cost to fix, but ballpark for me was between $50-150 for everything, part and labor.

I didn't know what the problem was, so while I was waiting to get it fixed, I kept the battery from draining by disconnecting it from the main fuse box. But be careful if you mess with the battery connections, don't touch hand to any metal - the spark when it connected and disconnected was a good reminder how un-fun it would be to catch that current with your body.

desperaterobots

Yeesh.

So, what's going on when I'm pumping my brake? When I stop the car, it's easy to completely depress my brake. The next pump, it's harder. The next pump, harder, and harder again. (I'm fighting hard here not make a sex joke.) That doesn't seem like a single 'part' to me?

Meanwhile I just asked how much a service would be. $430. Ouch.

EskimoDave

Have you checked your brake fluid?

edit - if you post what car you drive it might help.

desperaterobots

Haven't checked brake fluid. Will do tonight. It's a Hyundai Getz. Yes, yes, I know.

MrDelish

my brother's car got this symptom when he slammed the brake down and almost nailed someone on an icy road

I haven't the slightest idea of the technical details, but the little pressure thing behind the brake was pressed in so it wouldn't ever come out, and he had to take it to the dealer (still was on warranty)

Tallweirdo

I had the same issue with brake lights coming on when my car was parked and it turned out to be the brake light switch casing had cracked.

I called out the RAC (I am a member) and they were able to rig up a temporary fix using wire ties and superglue at no charge.

The car was already booked in for a service a week later and they replaced the brake switch module under warranty.

In the mean-time if you want to stop the brake lights from giving you a flat battery when parked you should be able to pull the fuse to stop the lights coming on. Just make sure you remember to put the fuse back in before driving again.

Edit: Car was a Hyundai Accent so it is probably the same part

desperaterobots

Hey! There's some nifty advice. How do I tell which one does the brake lights though?

Also, looked under the dash at the brake pedal. Had no idea what I was looking at. I've booked a service for next week. I'll mention it when I take it in.

tsmvengy

desperaterobots wrote: »

Yeesh.

So, what's going on when I'm pumping my brake? When I stop the car, it's easy to completely depress my brake. The next pump, it's harder. The next pump, harder, and harder again. (I'm fighting hard here not make a sex joke.) That doesn't seem like a single 'part' to me?

Meanwhile I just asked how much a service would be. $430. Ouch.

When the car is off, the servo or whatever the hell it is that mechanically multiplies your braking force is off. So when you pump the brake pedal when the car is off the brake fluid doesn't move around the system as it normally does, and so braking becomes harder.

desperaterobots

Okay. I would point out that when the car was new, I would not be required to pump the brake a few times for it to resist being pushed when it was off. Once it was off, you could barely depress the brake.

But I guess it's a moot point. I'm taking it in for a service, so hopefully they will figure it out. Apparently they need to change the brake fluid at this service anyway. Thanks for the suggestions guys, we'll see what happens in a few days.

RUNN1NGMAN

For future reference, you should change your brake fluid every two years regardless of how much driving you do. It's one of the more important parts of preventive maintenance and a lot of people overlook it for some reason (I know I used to).

saint2e

desperaterobots wrote: »

Okay. I would point out that when the car was new, I would not be required to pump the brake a few times for it to resist being pushed when it was off. Once it was off, you could barely depress the brake.

But I guess it's a moot point. I'm taking it in for a service, so hopefully they will figure it out. Apparently they need to change the brake fluid at this service anyway. Thanks for the suggestions guys, we'll see what happens in a few days.

Yeah if pumping the brake makes the resistance harder for a time, and the brake light to go off, I'm willing to bet that's the culprit. You've probably got air in your lines that needs to be bled.

The service should resolve the problem.