# 1990 GMC Sierra brake light



## Guap0_ (Dec 2, 2017)

Do you have an OBDII reader to check the codes? If not maybe Auto Zone will check them for you?


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## Mildman53 (Aug 17, 2018)

Already tried that and they were the ones who said I needed a new Module


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## Guap0_ (Dec 2, 2017)

Then why didn't you replace whatever it said was needed?


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## SeniorSitizen (Sep 10, 2012)

The problem may be at the brake pedal switch. Mine was and I adjusted is some way. I'm sorry but that was a long time ago and I can't remember what was required. I probably knew something in those days GM didn't know.
EDIT - EDIT - EDIT-I do remember lifting the pedal with my foot before exiting to turn the lights out before I discovered the problem and solution.


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## Nealtw (Jun 22, 2017)

I have had switch trouble with GM products.


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## SeniorSitizen (Sep 10, 2012)

Guap0_ said:


> Then why didn't you replace whatever it said was needed?


He was at Autozone. No more explanation needed.


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## Mildman53 (Aug 17, 2018)

I guess I should have been clearer. It is the brake light warning on the dash board that won't go out.


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## Nealtw (Jun 22, 2017)

Mildman53 said:


> I guess I should have been clearer. It is the brake light warning on the dash board that won't go out.


 I had a 91, that light came on and stayed on but went out for a day or two every 6 weeks or so. I wasn't about to spend the money for something like that. The guy that stole the truck didn't seem to care either.:vs_mad:


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## Guap0_ (Dec 2, 2017)

Not everyone at Auto Zone is brain dead. If the code said that it was the module why not replace it before you post here?


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## Mildman53 (Aug 17, 2018)

If read my original thread, I did change the module


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## Guap0_ (Dec 2, 2017)

Sorry, I missed that. After you replaced the module, did you erase the code with the OBDII reader or disconnect & reconnect the battery?


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## Nealtw (Jun 22, 2017)

Some of those measure the difference in pressure between front and back systems and can indicate a little ait in one of them.


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## Bigplanz (Apr 10, 2009)

What was the code? Is there a plunger switch on the brake pedal? On a Villager I had the plunger switch shorted internally and the brake lights stayed on all the time. Replaced it from one from junkyard and all was well.


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## ChuckF. (Aug 25, 2013)

Nealtw said:


> Some of those measure the difference in pressure between front and back systems and can indicate a little ait in one of them.


 I remember my old Mustang had a brake balance gadget that would turn on the brake light if it detected a difference in brake pressure from right to left. It was meant to detect a leak, but if it got out of whack you might have to bleed some fluid off from one of the sides.

I don't think they still use those, but you should look for a list of conditions that can turn on the brake light such as a full service manual would provide. Could be something on that list you have not thought of.


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## Nealtw (Jun 22, 2017)

ChuckF. said:


> I remember my old Mustang had a brake balance gadget that would turn on the brake light if it detected a difference in brake pressure from right to left. It was meant to detect a leak, but if it got out of whack you might have to bleed some fluid off from one of the sides.
> 
> I don't think they still use those, but you should look for a list of conditions that can turn on the brake light such as a full service manual would provide. Could be something on that list you have not thought of.


 I have just been trying to remember some of the stuff talked about when my light would stay on. It felt like everyone that should now was just guessing and I said to hell with it.


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## Nealtw (Jun 22, 2017)




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## Mildman53 (Aug 17, 2018)

I did the disconnect of the battery after putting in the new module. Little eerie of going back to auto zone! if you guys can keep thinking I would really appreciate it.


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## Douggerard (Jul 25, 2016)

I had a '95 gm truck that happened to. It was almost new when it happened so I took it to the dealer. I think they replaced a plunger type switch right near the brake pedal that turned the lights on when you press on the pedal.


Sent from my iPad using Tapatalk


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## ChuckF. (Aug 25, 2013)

Trace the hydraulic lines coming out of the MC all the way to the wheels and look for and identify electrical gadgets, except the ABS block of course. 

Get someone with a Service Manual on your truck or anything even close to get a list of 'conditions that turn on the brake light'. Check glovebox owner's manual. 

Is there a low brake fluid gadget on the MC?


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## Mildman53 (Aug 17, 2018)

Okay so I'm back. Did what a couple of you suggested and just said the heck with and let it go. So now it is flashing a code. Will blink 4 times pause a second and just keep repeating it over and over. Maybe not all AutoZone or O'Riley's are airheads but in this town nobody seems to know and am trying to stay away from high price dealers. Anybody know what the code means?


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## Nealtw (Jun 22, 2017)

These guys are talking about codes.
https://chevroletforum.com/forum/si...-flashing-morse-code-lol-but-seriously-50333/


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