Mysterious Brake Light Problem No One Can Solve

Maintenance/Repairs
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1

I have a 2000 Chevy Silverado pickup, V8, A/C, 105,000 miles, which drives like a top.

However, about a year ago, the TWO brake lights on the dash started coming on together, randomly. Sometimes the lights came on right after I started the first time, other times, they came on later in a trip after the truck warmed up.

The brakes worked perfectly, as far as I could tell. I took the pickup to the dealer, left it 2 days, and they checked the brakes, belts, tried everything (they said) including trying to get error codes on the computer. Trouble is, the lights had mysteriously gone out and refused to come back on.

A few days later, they came back on for me!! I could turn the truck off, wait a few moments, restart it, and the lights would go off, say, 80% of the time. Only to come back on later. So, I took it to a local Goodyear Tire store (while getting new tires) and they saw the lights, did a diagnosis on a computer, and got NO codes.

Now, I’m worried very much - you see, the brakes on this truck have never been changed! I’ve had them checked many times, always with the answer that they are still in great shape - last time, they had 30% left! I waited until the lights were ON, and drove all the way to the dealer; parked the truck running; and waited until a technician could come out and do the computer test. NO codes.

Now, I have noticed a possible pattern: when the weather is hot, as it has been most of last year here, the lights come on; when it’s cold, as it’s been lately, the do NOT come on. Just today, the weather warmed up into the 70s and, zap, the lights came on today.

Then, I thought, if anyone in the automotive industry could figure this mystery out, it would be Car Talk!

So, if you have any ideas or questions, please let me know. I’m about to either trade off a perfectly good vehicle, or probably spend a bunch of money for nothing.

Thanks.
Lyndon Evans

2

Is the fluid reservoir full? If it has remained full you might disconnect the low fluid warning switch to see if that eliminates the problem. The switch may be failing and erroneously signalling low fluid.

3

If those lights turn on when you turn the ignition switch from OFF to the RUN position then the trouble may be with the alternator. There is a test mode for the warning lights and it passes through the alternator.

4

By TWO brake lights, I assume you mean the ABS light and the BRAKE light? Have you checked the brake fluid level yet?

5

If you have adequate brake fluid, the trouble may be simply a flaky low fluid warning switch. When the lights come on next, pull over, open the reservoir, and jiggle the float. See if this action affects the warning light.

6

I had a bad switch in the master cylinder of my Olds once that made the light turn on. Couldn’t replace just the switch but had to replace the whole master cylinder. Like Rod Knox said, just unplug the switch to test it. Can’t believe the dealer doesn’t know this, it’s in the book.

7

Thank you for all the information. The fluid level has always been full. However, I may have been close to the solution without knowing it - once I jiggled the brake fluid container, which is sort of loose. I could have sworn that the lists stayed off after that for a while, but when they came back on, later, I forgot about the jiggle. I will try your suggestions today!

8

What TWO BRAKE LIGHTS? There is a Brake light that will illuminate if the float in the reservoir falls down on a low fluid level…it will light up your dash…what OTHER light are you talking about?

Blackbird

9

Maybe it is the one that looks like a yellow engine, the one that turns on when it is about to break - hence the “break light”.

10

Very funny! The two lights are the ABS and the usual brake light warning. I tried all suggestions this afternoon and nothing made any difference. Took the truck to the dealer and told them to find the problem and fix it or I’m trading it in on a new Tahoe!

11

“Took the truck to the dealer and told them to find the problem and fix it or I’m trading it in on a new Tahoe!”

Now they have absolutely no reason or incentive find/fix the problem and won’t give you squat for a truck with an “undiagnosable” brake problem.

12

Yeah, fix this truck or else…

… I’ll buy another one from you.

13

Nope, the dealer could not duplicate the problem! No codes, no nothing. Told me to bring it back in again when the lights are on and they will put it on the computer (3rd time.)

However, I love my truck, so fixed the A/C and am determined to figure out what’s with the brake lights.

There is a possible clue, but I know nothing about it: they found that the emergency brake was not working, and had to have several parts replaced. Do you know if that brake is connected to the two warning lights in question? THEY said it was not, but I do not think I’m talking there to the sharpest knife in the drawer. I’m sure I’ll find out after I pick up the truck tomorrow!

14

I think at 105k it is time to do a brake job. The outer pads may look good, but the inner pads may be worn, and they may not check both.

15

The dealer replaced the rear brake pads and the emergency brake pads. Finally got code for brake lights, which told them I had a bad electronic brake control module for the anti-lock brakes. Then, they told me the cost - $1500 !! I live in the south where it rarely freezes up, but sometimes rains a lot. I’m thinking about ignoring the intermittent lights and remembering to pump the brakes should I go into a skid. What do you think about this? Thanks.

16

That is a sound idea. Many car owners do the same thing – when their vehicle reaches a certain age they decline to make costly repairs on the ABS.

If you lived in Canada that might be unwise. But since you live in the south I think you have reached a reasonable decision.

17

I would basically fail to trust the dealer’s diagnosis. There aren’t any codes that will tell you directly that a part is bad. And the thing is that if they go replace it at $1500 and problem persists…well, you won’t get your money back. If this module was actually a real problem the issue could be random & intermittent like this - but probably not. I’d be banking a loose/damaged wire.

18

Thank you for your input! Now that I know there is a specific module in question, I will find it, and look for bad wires, loose connections, etc. And, keep my $1500 for my next car! Thanks to all, this is a “real community!”

19

Problems like this are usually due to a simple bad connection somewhere. You may be able to find it by tapping on suspected trouble areas with a screwdriver handle.