Brake system warning light on dashboard

SIRJR

MEMBER
1995 CHEVROLET LUMINA
6 CYL
FWD
AUTOMATIC
102,000 MILES

The red 'brake' light has been coming on and off for the past month. When I start the vehicle, the light comes on, then goes off as it is supposed to do. After driving for about five minutes or more the light comes back on and will stay on for a few seconds to a few minutes during the entire drive. There are some times when the light does not come on at all. The brakes work fine, the pedal feels normal, there is no leakage of brake fluid on the ground. The vehicle has ABS. The owners manual states that when the light stays on, it indicates brake system failure; however, the braking system is working normally. I have been in vehicles when a brake line has broken, so I know (fortunately/unfortunately) what happens with a partial brake system failure. Please give me advice on what I should be checking to find out what is causing this brake light issue. You have helped me with other issues with this vehicle and now I am back again! Thank you.

6 Replies

CARADIODOC

MECHANIC
33,916 POSTS

Only three things will make that one turn on. The fluid level is low in the reservoir, the parking brake is not fully releasing, or there is a leak in one of the two hydraulic circuits.

GM has a really weird master cylinder design. If there is a leak in the hydraulic system, a valve trips in the master cylinder to block the port to that front wheel and the opposite rear wheel. The brake pedal will feel normal, there will likely be no brake pull, and the fluid level will not go down, yet you are supposed to know something is wrong.

If the parking brake is not fully releasing, typically due to a sluggish cable, you might be able to observe a clue by watching the warning light. With the engine off and ignition switch on, watch the brightness of the light very closely while you apply the parking brake. If you see the very slightest change in brightness when you apply the brake, that switch is working properly and is not the reason the light is on.

If the fluid level is low, add a little clean new fluid but do not totally fill the reservoir. If the light goes out, the fluid was low either because of a leak or the front disc brake pads are worn and need to be replaced. Doing so will require re-seating the caliper pistons to make room for the new, thicker pads and that will push the fluid back up into the reservoir. That is why you should not totally fill it.

If the fluid is not excessively low, unplug the level switch in the reservoir. If the light goes out, the float for the switch may have sunk.

Finally, unplug the wire from the combination valve below the master cylinder if there is one. The pressure-differential valve part of that assembly is in the master cylinder but I cannot remember where the switch is. If that makes the light go out, look for a leak in the hydraulic system.

Caradiodoc

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Tuesday, December 14th, 2010 AT 5:23 PM

SIRJR

MEMBER
86 POSTS

Thanks for the information. I will start going through your check list and get back to you regrding my progress. I greatly appreciate your expertise.

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Tuesday, December 14th, 2010 AT 8:04 PM

SIRJR

MEMBER
86 POSTS

I added brake fluid to the reservoir. It was slightly low; however, I replaced one of the front brake hoses this year and after bleeding the system, I do not think I filled the reservoir to normal capacity because it is hard to not only access the reservoir, but to fill it with fluid. Also, there is no little window to view the fluid level. This time I back/side lit the reservoir and rocked the vehicle back and forth to see the level of the brake fluid. The light went off and has stayed off for three days. I will see if this resolves the issue, if not, I will continue with the rest of your recommendations. The parking brake switch works fine as I noticed the change in light brightness as you stated. Thanks for all the great advice!

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Saturday, December 18th, 2010 AT 3:47 PM

CARADIODOC

MECHANIC
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Good to hear, please use 2CarPros anytime we are here to help.

Best, Caradiodoc

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Saturday, December 18th, 2010 AT 7:53 PM

ALANG62996

MEMBER
1 POST

I've got a 2000 Chevrolet Lumina that is currently in the shop. The brake light is still on after a brake line has been replaced, and all brakes have been bleed. My brake pedal still goes down to the floor, and idea on what else the issues could be?