I recently bought a '90 Suburban off a buddy of mine at work and am trying to work out a few bugs. One that just started this week is that the brake warning light came on the other day when I had it in for an emissions test and now it won't go out! I have tried all the things I can think of, but I'm not sure how many devices could actually turn it on. The truck has no anti-lock brakes or anything, so it should be pretty easy, so what am I missing?? I've tried disconnecting the electrical connections at both the prop valve and the ebrake pedal switch, but the light stays on! The ebrake pedal switch is way up on top of the assembly, but looks to be operating properly. With the ebrake switch hooked up, the light will actually get brighter when I press the ebrake lever, so I think that switch is working right. disconnecting the prop valve wire does nothing. What other connections could be causig this? What am I missing??

Thanks guys,
Bill C.

No schematic so I can't look anything up. *Stab in Dark*
Any sensor on the M/C for low fluid?

Nope, checked for the sensor and the fluid level... no sensor and fluid level is full.

Bill C.

Bill,

I went throught the same situation with a 90 gmc jimmy S-15. The brake light would turn on when ever it got really cold and stay on. I would reset it and would come back again. But in the summer it would stay off. Go figure. I at first at thought maybe there is a sensor that affected by temp or corrision. I never did figure it out and gave up trying (brakes worked great). And I did chase the e-brake light route also. Same result you had.

Perhaps the computer is seeing a bad ground somewhere and tripping the light? Go to Autozone and have the code read. I jumpered mine but it flashed a worthless code that did not help in diagnotisc. Good luck. - John

Well, it's not cold here John... in fact, been too hot lately!! It ain't supposed to get this hot in Colorado!!

You mentioned resetting the light... how did you do that? mine does not come and go... it is on steady from when you turn the truck on till you turn it off! I'd like to hear more about this resetting it!

Also, wouldn't the 'check engine' light be on if there was a code to read?? I'm not much on the computer controlled stuff, so any pointers there would help also!!

Thanks,
Bill C.

My .02...

As my profession is diagnosis of machine problems...reading comments such as yours that it happened after it was in a 'shop' lead me to believe the 'technician' probably found you a loose connection while under the hood (they're under the hood in Portland, the last time I went through).
You have the unfortunate job of finding a bad circuit or ground (maybe as simple as a corroded pin connector).
My gal's LeBaron will ping the damned low-gas warning dinger continuously with the lights on when one of the front turn signal bulbs burn out...go figure.

Keep an open mind, and mark fusible links (when you come across 'em) with bright colored electrical tape to make 'em easy to find next time smile.gif

fyi, in returning the favor, I searched, and did find a couple good forums, but didn't send links as I'm sure you already searched for them. Found nothing on the brake light, except one unanswered post, and a couple on ABS lights. One interesting one was in regards to a 'height-sensitive proportioning valve', but no mention of brake light issues.

Also found out that Chilton's is now online, and with schematics here
http://www.cybrrpartspro.com/Manual%20Lookup/cal_ModelLookup.html


Good luck!

JR

BC, I am pretty sure that Sub has rear anti-lock and although I don't know how to get the codes, someone here probably does. My 90 Full size Blazer had them too, so I think the Sub does.

Bill,

I reset the light by disconneting the battery and pulling a certain fuse and re-inserting it after 5 minutes or so. I think it was fuse marked ECM brake but I can't be certain since that was two years ago. Keep in mind this was the S-15 version.

The brake light on dash would flash a code if you jumped the diagnostic port. I suggest getting a Chilton or Haynes (the library should have them) and looking at the brakes section. They should help you eliminate possiblites quickly. If you have a Autozone or equivelent that will scan the computer for you for free, pay them a visit. Good luck.

I can't find the schematics on that site. Probably just me.
Bill
If you want and do find them, send me the area covering the brake light wiring and I'll see if I can spot anything.

Bill,

I checked the link to chilton above. If you go to rear wheel anti-lock brake section; system and diagnotic testing; click on figures. What model do you have?

Well guys, unless I'm missing something really important, I'm pretty darn sure that this truck does NOT have anti-lock brakes... even rear ones! Wouldn't there be some kind of sensor or something at the rear wheels? I rebuilt the brakes about a month ago when I first got the truck and the brakes have worked great ever since! They still work great! Even with the light on! Also, there are no wires at all going to either the rear diff area, or to the rear wheels areas, so none of that load-sensing valve stuff on there either. It seems very basic, just can't figure it out! I'm thinking the computer or ECM has a hick-up or something and will try 'resetting' it via John's method. I'll keep you guys posted if I think or discover anyting!

Thanks,
Bill C.

Cool!! Looks like resetting the ECM (disconnecting the power!) did it!! No more light on now. Hopefully it won't come back.

Thanks,
Bill C.

BC
I have a 90 pick-up with rear wheel anti-lock. There are no sensors at the wheels. It is a pressure and speed monitoring system. There is a large rectangular black electronic module attached to the first proportioning valve next to the MC.

Rene

Originally posted by BC:
Well guys, unless I'm missing something really important, I'm pretty darn sure that this truck does NOT have anti-lock brakes... even rear ones! Wouldn't there be some kind of sensor or something at the rear wheels? I may be mistaken but I think the sensor is on the pumpkin and the sensor ring is around the ring gear. It's a primitive system and I don't think it works real well but Big Brother said all trucks had to have rear anti lock. Not sure of the year but it's right around your '90.

Jeff