90k5 brake light issue

[malignd1]

Alright, i've done some scouring trying to pinpoint my current problem with the 90'k5 but cannot seem to get a complete resolution. I finally got the exhaust done to get her in and to pass emissions. She did fantastic as her numbers were less than 1/2 the legal amount now; b4 exhaust and egr valve replacement numbers were more than doubled so i am now really excited about where she's goin. But that isn t the problem.
It seems at right about 36-37mph the in dash brake light comes on and stays on until the ignition is turned off. It has been this way since I purchased the vehicle 8/2010. However, i noticed that if i lift up on the brake pedal the light will turn off, only to turn back on almost instantly, but only when speed exceeds 35mph. I've read posts in the forums where people have had a similar issue but can't seem to find a resolution and the threads end before actually stating a fix for it. I can drive around all day and it will never turn on unless 35mph speed exceeded. This has been frustrating at the least but on top of that, the other day when I was leaving the smog testing center the dash light came on and was blinking 9 short flashes and 1 long flash, over and over and over again. Even after turning the ignition off then back on. I let the truck sit overnight and went out yesterday and the flashing was no longer happening. FLuid level good; brake feel good; brake function seeming good...no issues. Im not a mechanic but am mechanically inclined but have limited resources. I wanted the truck to have something I can work on and could fix myself. Not that that's all that important but just thought id throw that in there for good measure. Any thoughts can help.

 

[Fordum]

Well, I'm down with a high fever right now, so I'm not as sharp as usual, but if it goes out when you lift the pedal, then it sounds like there is a problem there.

Probably the brake light switch is slightly out of adjustment and is staying on, so the truck thinks you are riding the brake or there is something wrong with the switch so its trying to warn you.
You need to either adjust the brake light switch or put a stronger spring on the pedal.
GM had a problem many years ago with the switches stripping out. Back then they had plastic threads and screwed into a mount.
After a few years of the pedal hitting them when it was let off, they would get pushed back.
I seem to remember there was a kit with a nut and/or collar that fixed that, but its been a while, and it hurts to think right now.

 

[NEWMEXICOK5]

well if the light count is right that should be code 9. its a rear speed sensor problem. and that would make sense if the light comes on after 30 miles an hour

 

[dremu]

For older trucks, the brake light comes on for two reasons:

One, the parking brake lever has a switch on it. If that switch gets bunged or the wiring is frayed, that might do it.

Two is the combination valve, if there's a sizable difference in pressure from front to rear. This will usually be caused by a leak, but can also happen during bleeding. The combo valve has a reset button.

However, 1990-91 trucks have a THIRD cause for the brake light, the ABS system. It only functions in 2WD High and only on the rear wheels, so it's also called RWABS (rear wheel anti lock.) My experience with it was negative, as has been that of many people.

You can disconnect the ABS computer by unplugging it; it's up front on the brake booster/master assembly, and the wiring to it is pretty obvious.

Should you be so inclined, you may choose to get a service manual and look up the ABS code, then start dealing with whatever's wrong, the sensor(s) or the like.

-- A

 

[smier]

If you can verify that EVERY component in the brake system is working properly, I vote for unplugging it. If you have ever experienced the ABS systems lackluster performance on slick roads, you may want to unplug it and forget about it. I wonder if gm ever real world tested thus setup? I had a couple exciting moments with my abs in my '91. One was doing a 5 mph slide down a hill, THRU a stop sign and busy intersection, all the while trying to keep the front wheels from locking up so I could steer while fighting the pulsing an surging rear antilock brakes!!! I normally don't recommend disabling stuff on vehicles, engineers put them there for a reason, but in my personal experience, the abs on these trucks is more dangerous in severe weather than without it. Unfortunately, I am one of those people that has to report for work even in a state of emergency, so I'm often on the road before the plow trucks in the winter time. My '89 and '90 s10 blazers had the same systems, and they sucked from brand new!

 

[malignd1]

So, I climbed up underneath dach and found the switches. White plastic button type thing but actually say 2 in there. Anyway, took and srcrewed em in just a turn further and have yet to see the light come back on so we'll hope that was ma problem. Thanks for the input. Ill post anymore findings or issues if and when.
Thanks abunch!