GMC Repair: Brake warning light at 35 MPH, brake warning light, power brake booster

Question
QUESTION: I have a 1990 2500 Pickup, AT, 2wd 350. the brake/ ABS warning light was flashing a 10 code. I replaced the Speed sensor and had no change, then I replaced the ABS Control Module and the symptom changed. now the Brake/ abs warning light will occasionally come on when I hit 35 MPH. It will turn off when I brake and the truck slows below 20-25 MPH and will come on again when I speed up above 35 MPH. sometimes the light never comes on at all. Lastly, the entire brake system has been replaced about a year ago including proportioning valve, Master cyl., Power Brake Booster, calipers, pads, drums, ect. and has been working perfectly until now. I can not pull a ABS code because the Brake / ABS light goes out when you stop. lastly this problem seems more pronounced when the truck first hits 35 mph. after you stop accelerate quickly beyond 35 MPH the problem likely will not reoccur until the next day.

ANSWER: Hi
Just from what you state, I'd have to say you MAY have a faulty module.
If iy does the SAME thing, once a day, everyday, first drive cycle and then it is OK the rest of time, that sounds like it MAY be programmed wrong. As those units are preprogrammed, this is why I would think this.
It has been a while since I diagnosed this system, but I THINK you can use certian scan tool(s) to retieve data and watch data from EBCM. I Know we had to use different cartridge and adapter with old Tech 1 scanner.
See if you could/can find someone in your area that'll be able to watch data.
See if a Whees speed sensor is dropping out, but if not, I am GUESSING you may havce a faulty EBCM.
Just advice from experience.
Hope it helps
Good Luck
Paul

---------- FOLLOW-UP ----------

QUESTION: I re-replaced the speed sensor and no change, But I did notice a couple different symptons I over looked earlier, This Brake Light will always come on the first time you go over 35 after you start the engine, if after the light comes on, I put the gas pedal to the floor and accelarate quickly, the light will go out and will not come back on unless the engine is turned off and back on again.the light will also go out after you come to a stop and take off again. again, it will not come back on until the engine is shut down and started again then accelerated above 35 mph. Lastly is the EBCM the same as the ABS control Module? again I just replaced it with a new one last week.

THanks again
Larry

Answer
Hi Larry
Are the rotors new?
If not, remove rotors and clean all the speed sensor rings and speed sensor.
Again, if you can find someone with the older scanner, maybe you can watch data and see if any speed sensor is dropping in and out.
Was it doing this BEFORE the ABS Module was replaced?
Yes, the EBCM (Electronic Brake Control Module) is the same and the ABS controller.
Thanks
Paul