GMC Repair: 2000 GMC SIERRA 1500 6 CYLINDER, gmc sierra, brake failure

Question
QUESTION: BRAKE FAILURE AT ONLY SPEEDS OF 5 TO 6 MPH. ABS LIGHT CAME ON FIRST TIME IT HAPPENED, DROVE IT THE NEXT DAY AND NO ABS LIGHT.

ANSWER: By stating brake failure, are the brakes totally inop (to the floor and no stop?) or is just the ABS light on?
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Pawl

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

QUESTION: the abs light is not on anymore, it just that the brakes will not stop at five to 6 mph.When i try to brake at that speed, the truck continues to keep rolling. At other speeds no problems. checked around calipers, master cylinder, and booster [no signs of leaks and not loosing any fluids]. If i pump the brakes and hold them, the pedal does not travel to the floor. Around the same time of this problem the service engine light stays on. Thanks for your help

Answer
Hi
Do you hear any hissing noises?
If so I would suspect the booster internally failing at high vacuum.
Does your truck have rear calipers?
If NOT check the wheel cylinders at the rear brakes.
If all this checks out It is possible that the ABS Pump MAY be internally bypassing. I have run into this a few times.
Get the codes scanned for Service Engine light AND see if there are any codes stored for the ABS system at same time also.
I Hope this helps
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Pawl