Brake Warning light

[Mark D]

Was seaching on forums and came across this thread.
Brake Warning Light Problem
I have same problem. This is where I am right now.I have done what crabtruck said shown below iand I have a 4 code showing.

Originally Posted by crabtruck

Good Jessie, now we're making progress.
The wiring and parts are different for a burb which I know you don't have,
but i wanted to make sure you're not driving a Canadian/DRL version also.
The following assumes your not, don't be fooled by having a DRL fuse socket, not same thing.

Brake light should come on at key up for about two seconds then go off.
Since yours brightens by itself, then doesn't get even more with use of e-brake (which should be brightest condition),
you need to disconect ebrake switch. If light goes out, you found the problem.

If light still on you need to pull the RWAL-CODES, not check-eng-codes.
This should only be done while the brake light is on or a false code (9) will be stored and the rwal will be disabled until reset.
This method is for RWAL and not 4WAL (on burbs, which you don't have)
With key on, ebrake off, brake light on, jumper the ALDL connector
from pin A (ground, upper right, corner) to pin H (speed signal, lower left, near corner)
After the pins have been jumpered for about 20 seconds, the BRAKE light will begin to flash.
Count them begining with the long flash as 1 followed by the short flashes as 2,3,...
The first set of flashes may be wrong (too short) but the repeats will get it right.
Valid codes are: 2,3,4,5,6,7,8,9,10,13,14,15
Later reset of RWAL DTCs is by: key off, pull stop fuse for 5 seconds.
That's the "memory" hot to EBCM (rwal controller). EBCM also gets power from speedo/rwal fuse.

If no code found, remove jumper and measure voltage from ALDL A to H.
For this type RWAL, it should be 8 to 15 volts.

If you get zero volts check for physical wire problems for EBCM under hood and VSS buffer in cab.
Unplug EBCM 6-way (not 4-way) and measure 6-way plug D to A for 8-15v.
I'm expecting this to be right since you didn't mention any speedo problem.
Do verify that the "A" wire is actually getting a good ground.
Measure "B" to "A" and "C" to "A" for 8-15v also (two hots to EBCM)

Light should be off at this point, if not, you have a simple short to ground.
You can follow the "E" from EBCM plug (tan/wht) as it splices with combo valve wire and heads for bulkhead "H3"
then comes to a diode set that, after they join, goes to light.
The second diode of that set goes to e-brake switch and DRL pre-wiring.

If both B and C measure 8-15v, reconnect 6-way plug.
If light stays on, probably bad EBCM, don't replace without doing the code thing first.
Also may consider not replacing, since it is only part-time on that truck anyway.
If light turns off, check for short in 6-way connector or harness.

Hope that gives a little to work with, good luck and let us know what you find.

[Mark D]

I should probably say what I have.
1990 Chevy k1500
all new brakes rotors, pads, drums, shoes and master cylinder.
Whole system has new fluid and the light was on prior to doing brake job.
Mark

[Mark D]

Also should mention that I have reset the code and light goes out for only a few seconds than come back on when rechecking it is the 4 code.

[Case 7230]

Acording to my book code 4 is a grounded reset switch circuit. The reset switch is in the anti-lock brake combination valve. This should be below your master cylinder. Try unplugging the electrical connectors and cleaning them.

[Mark D]

Thanks for the response.
I just got back in, will give it a try in the morning.
Right now it is pouring out, been having off and on thunderstorms around here all day.
Mark

[Mark D]

Case 7230 thanks for the info, it was not the connections. It was the switch. I changed it out and now all is good. Thanks again.
Mark

[Case 7230]

Glad you got it fixed.

[gmctrucks]

Mark D Welcome to the club that a good write up you found and posted that's 5 points for you.
Be good! GMC