Brake light

Tiny
MANUOY
  • MEMBER
  • 1990 GMC SIERRA
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 106,000 MILES
My emergency brake light started coming on all the time. Somewhere I read that it could mean your brake fluid is low. So I got some but I did not have to hardly put any in. So there must be something else going on?
Monday, March 26th, 2018 AT 8:00 PM

3 Replies

Tiny
CARADIODOC
  • MECHANIC
  • 33,873 POSTS
Check that the brake pedal is all the way released.

Is this the red "brake" warning light? Does the truck have anti-lock brakes?
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Tuesday, March 27th, 2018 AT 9:51 AM
Tiny
MANUOY
  • MEMBER
  • 2 POSTS
Yes it is the red "brake" warning light and I have double checked that it was fully released and no it doesn't have anti-lock brakes
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Friday, April 6th, 2018 AT 9:14 PM
Tiny
CARADIODOC
  • MECHANIC
  • 33,873 POSTS
Sorry for the brain fade. I should have said, check that the PARKING brake pedal is fully released. There's three things that can turn the red "Brake" warning light on. Low fluid level is one of them, but only if that option is on the vehicle. A stretched parking brake cable, or one that's rusted in the partially-applied position won't pull the parking brake pedal all the way back. That will keep the light on. A trick to see if that is the problem, assuming your parking brakes work properly, is to watch the brightness of the warning light. If something other than the parking brake has turned the light on, it will get very slightly brighter when you apply the parking brake. That will be real subtle so you have to watch it closely.

The third switch is in the combination valve on the left frame rail. Follow the steel lines from the master cylinder to that brass block. You'll see a single wire attached to that switch. It only trips if there's unequal pressures in the two halves of the hydraulic system due to a leak. Just unplug that wire. If the warning light turns off, we'll need to discuss how to solve that.
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Saturday, April 7th, 2018 AT 6:51 PM

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