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While I'm driving in my Toyota Corolla 1999 (3-door model): My parking brake light randomly turns on and off while the car is moving. It doesn't go on and off rapidly, but usually switches at a random interval of 15 seconds to several minutes at a time. When the car stops: The light no longer toggles.

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This started happening all of the sudden in the middle of this summer. It seems like it is slowly getting worse, because the light is now more on than it is off.

The car is in a cold environment far up north in Norway (We are already below 0°C).

The brake feels normal, and was changed 2 years ago. Both the pads and the disks themself. However, the parking brake is very slack and almost non-functional. So could it just be a confused sensor? I don't use my parking brake at all since I always park on flat areas and usually just leave it in first gear.

I don't know much about cars at all, so avoid the terminologies if you can.

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As well as being a parking brake warning light, that is also a service brake warning light - i.e. it warns you of problems with the main footbrake.

Given what you have described, my first thought would be to check the brake fluid level - if it is near the 'min' mark, you will need to top it up from a fresh, unopened container. If it is empty, or below the 'min' mark, there is a risk that air could have got into the system, and so I'd recommend getting the system bled through. (Also, if the fluid hasn't been changed in a long time, it's worth getting it changed at the same time)

  • This was indeed the problem. The fluid was shy of over the min mark. I guess it's true what they say about Toyotas, that their sensor is very sensitive. But why did the fluid become so low? Do I have a leak I need to worry about? Or is it just vaporized, since it took very long to reach that level it was on? – Alexander Johansen Oct 16 '16 at 17:04
  • I would thoroughly inspect the entire system for any signs of leaks - especially all the cylinders and the joins in the pipes, and keep an eye on the level for a while - it's possible to have a leak somewhere you can't see it... – Nick C Oct 17 '16 at 7:32
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However, the parking brake is very slack and almost non-functional. So could it just be a confused sensor?

This is very possible, and I observe exactly this at the moment with my car. Typically, the parking brake lever acts on the brakes via cable pulls. Small springs at the brakes ensure that the brakes are released and the cables are pulled back when you lower the parking brake lever. The springs also hold the lever down, and are responsible for most of the force you experience when pulling the lever.

One failure mode is that the mechanism at the brake seizes. While you are strong enough to pull the brake, the spring is not strong enough to release it, or to pull back the cable. As result, the lever is slack and isn't hold down properly. When it moves a little, the sensor thinks the brake is engaged, and lights that light.

When you observe this the next time, try to push down the lever and check if the light goes off. If that's it, just get your parking brake fixed.

@Nick C wrote it could also be a warning about a low brake liquid level. This sounds reasonable, and you should check the level. But since you mentioned the nonfunctional and slack parking brake, I'd bet on this.

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