Emergency brake light stays on?

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My emergency brake light stays on even when the brake is off. Could a fuse be faulty or a sensor be rusty? Any other cause you can think of?
Sunday, November 11th, 2012 AT 12:48 PM

1 Reply

  • 33,738 POSTS
There's three things to look at. First, it is possible for the parking brake light switch to be snagged, then pulled and bent out of shape. It's basically a flat piece of metal that's pressed on by the released parking brake pedal. To prove it, you can unplug that switch.

Second, the same warning light is used for the "pressure-differential switch. That activates when unequal pressures build up in the two halves of the brake's hydraulic system. That occurs when there's a leak in one of those halves. The leak could be external where you see brake fluid on the ground or on the back side of a tire, or it could be internal, meaning leakage inside the master cylinder. With an internal leak, the brake fluid level won't go down over a short period of time. With an external leak, the fluid level will drop in the reservoir. While not shown on the diagram, many models have a third switch in the reservoir to indicate low fluid level. That also turns the red warning light on.

The pressure-differential switch is in the middle of the combination valve on vehicles without anti-lock brakes. That valve assembly is right below the master cylinder with two steel lines running between them. That switch can also be unplugged. If that makes the warning light turn off, the cause of loss of braking power in half of the system must be diagnosed and repaired. On GM and Chrysler products, that valve is spring-loaded to reset on its own, but they often stick. A good hard jab on the brake pedal will usually free it up.
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Thursday, December 24th, 2020 AT 4:03 PM

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