Brake light

[cinquecentoe]

Brake Light

Hello everybody,

I live in Germany and own a 1990 Chevy Blazer 5.7 ltr.

I am experiencing problems with my electric system. Suddenly a few
weeks ago after the winter sleep the "brake" warning light came on and did not turn off. Brake fluid is o.k., brake pedal switch is o.k., brake pads are o.k..

A friend checked the computer by connecting pole A and H on the ALDL,
the code showed nine flashes. We changed the speed sensor in the transfer
case, but the light still comes on after having reset the computer. It takes
approximately 1 1/2 miles before the light turns on again.
I ordered the "transfer case switch" for a try as it seems to be rotten.

Anybody has any idea what causes the brake light to come on and stay on ??

Regards from Germany

Alex

 

[Leper]

Unplug the controll box on the side of the master cylinder for a few seconds and plug it back in. Mine does the same thing every few months.

 

[1985_K5_Silverado]

Have you really looked underneath lately for any brake fluid leaks, anywhere in the system?

 

[goldwing2000]

Did you try resetting the switch on the combo valve?

Is your e-brake switch acting up?

If you don't have ABS, the only two things that should turn that light on are the e-brake and the combo valve.

 

[cinquecentoe]

The truck has ABS on the rear wheels as far as I know, it is stock,
no modifications made.

We disconnected the upper of the two connectors on the ECU close to the master cylinder and reset the computer by connecting A and H twice for
2 seconds.

That only lasts for 1 1/2 miles until the brake warning light comes on again.

The combo valve, is that the switch on the master cylinder ?? We checked
it and it is in working order, as is the brake pedal switch and park brake
switch. Really no leaks under the truck, the fluid level is approx. 1/2 inch
below the cover.

Do I have to drive the truck after resetting the computer for a certain
mileage at a certain speed, or is the resetting enough ?? We did
reset the computer and then I drove for 6 miles above 45 mph. That lasted
for maybe 30 miles before the light came back on again. ????

Any further ideas ? Please help.

Regards from Germany

Alex

 

[Jagged]

After you reset the light... turn the engine on and press the brake pedal as hard as you can. Does the light come back on?

The seals inside your master cylinder might be going bad.

 

[cbbr]

Maybe tht's my problem - my brake light comes on from time to time for no good reason. The pedal gets soft also. Pump it for a minute and it back to normal. I just assumed that there was a bubble in the line.

 

[goldwing2000]

Weird. I didn't know Blazers had ABS in '90.

Anyway... the combo valve should be on the back side of the forward-most frame crossmember. Just follow the lines down from the MC and see where they go into a big junction block. That block should have a rubber cap on one end. If you push in on the rubber cap, it resets the spool on the pressure differential warning switch.

If that's the cause of the light, then you have to figure out why you're getting enough pressure differential to trip the switch.

However, that won't normally come on just while driving.

With the symptoms you describe, chances are you have either a bad rear wheel speed sensor or excessive resistance (corrosion) in the wiring harness going to the sensor. I know you changed a sensor in the t-case but (since I'm not familiar with that specific system), there might be another sensor located either on the axle or in another location on the output.

 

[cinquecentoe]

Hey guys,

yesterday we checked once more the brake light situation. We read out
the computer with a scanner tool (CP 9001) and reset the computer by
disconnecting the stop/hazard fuse on the fuse box.

Since then the light did not turn on again (for maybe 30 miles now).

It seems that there was a problem in connection with a wrong connection
of a seat heating device I had installed last summer. It had been connected
to the cables that come from the 4WD shift indicator. That seemed to have caused the problem.

Hopefully that will last now.

Regards from Germany

Alex

 

[cinquecentoe]

Hello again,

after the last reset the luck lasted for about 200 miles til the light came on
again and stayed on continously til it got worse when it started flashing
code 9 over and over again while driving.

I went to see the GM dealer here in Stuttgart and they found out that
the purple cable that goes into the ECU did not show any voltage. So
they put a new cable parallel to the old one. I hope that was it .

Regards from Germany

Alex