1991 Eldorado brake system

[Andrew Armitage]

The “BRAKE!” light is illuminated on my dash. And ABS light comes on after the first time I hit the brakes while moving after starting the car.

I just changed all 5 brake hoses along with the rear crossover brake line, the right rear caliper, the front left line from the caliper to the ABS, and a new master cylinder. All 4 calipers have been bled. The fluid is topped off. The rear proportioning valve was reset when I replaced the rear crossover line (ISO bubble flares on all line connections per the shop manual). The E-brake is not set. No leaks. Every connection is dry.

The brake light was on before I started on all this work. ABS light wasn’t. That started after.

Any other ideas of why the brake light is on?

[TJ Hopland]

Is this got the 'normal' master cylinder and booster then the ABS is a completely separate assembly or is it the all in one electric TEVES system?    If its the TEVES I do remember reading some very specific and unique procedures to bleed things.  If its the regular system then I don't think they were smart enough to know if they got air in them you just get a mushy pedal. 

Does the light just stay on or can you get it to go off but after some brake or key cycles it comes back on? 

[Andrew Armitage]

Master cylinder has lines that run to the ABS module and then from the module, 4 lines run to the wheels.

I was thinking maybe ABS module needed to be bled?

Red brake light is on all the time. ABS resets every time I start the car but illuminates after I step on the brake for the first time while the car is in motion.

[TJ Hopland]

The light coming on when you start to drive kinda points to a wheel speed sensor issue.  I don't think its an open circuit (unplugged or damaged wire) because that should get caught with a power on self test.   Its got to be that a signal just isn't there or its out of range.    You could do a physical inspection looking for anything that looks out of place but I suspect finding someone with the proper scan tool would be the real way to find the problem sensor.    Those earlier ABS systems didn't always connect to the main data link, they often required special cables that plugged into their own connector so in addition to having the correct software you need the correct cables.   I think GM were somewhat universal so maybe it won't be that bad but some other makes apparently had a different cable for every model and every year.

As for the regular light you will have to get a service manual and see what can turn the light on and go through the troubleshooting for each thing that could possibly doing it.   My newest manual is a 90 and that was still the TEVES which was a much different animal so I doubt anything I could read would really apply to yours.   Since that was the first year for a new ABS system maybe there is some other thing that turns the light no we would not normally think of.

[V63]

TEVES should be a 4 letter word 🤬, been there done that! Save yourself!

[Andrew Armitage]

The light coming on when you start to drive kinda points to a wheel speed sensor issue.  I don't think its an open circuit (unplugged or damaged wire) because that should get caught with a power on self test.   Its got to be that a signal just isn't there or its out of range.    You could do a physical inspection looking for anything that looks out of place but I suspect finding someone with the proper scan tool would be the real way to find the problem sensor.    Those earlier ABS systems didn't always connect to the main data link, they often required special cables that plugged into their own connector so in addition to having the correct software you need the correct cables.   I think GM were somewhat universal so maybe it won't be that bad but some other makes apparently had a different cable for every model and every year.

As for the regular light you will have to get a service manual and see what can turn the light on and go through the troubleshooting for each thing that could possibly doing it.   My newest manual is a 90 and that was still the TEVES which was a much different animal so I doubt anything I could read would really apply to yours.   Since that was the first year for a new ABS system maybe there is some other thing that turns the light no we would not normally think of.

You sir, were correct. Front left and right wheel speed sensors are bad. I remembered I had a brand new ABS scan tool that my Dad gave me about 15 years ago.

https://youtu.be/pMl7wBvzDrE

Seems the sensors are pretty unobtainable. Someone from another forum started that VW of the same vintage used a compatible part as they used the same ABS module. I’ll have to look into it.

[TJ Hopland]

Cool about the tool.  I had no idea that it was that simple similar to reading engine codes.   The tool must just short some pins or insert a resistor in the right place to push it into the different modes.   

Didn't know that abs sensors were hard to find.   Seems odd you would have thought those would have been common to many GM's but I suppose that was a little early for ABS to be super common.