GMC Brakes Go To Floor- ABS Light On

Live Chat: The abs warning light has been intermittently coming on in our GMC Jimmy 2000. Today the brakes completely quit working during a stop. The regular brake warning light never has/did come on. Placed vehicle in park, turned off engine, and restarted without further incident, except of the abs light continuing to light periodically. Taking the truck to have codes read, three were found. Two for the front right wheel, and on for the rear right wheel. All three pertaining to sensor failure or intermittent failure. Wouldn't there need to be something wrong besides a sensor, for the brakes to fail?

 Answer:Did the pedal go all the way to the floor with no stopping power, or was the pedal sort of bouncing / fighting back.

It was a little of both. At home later, we turned the engine off, checked the brake fluid level, and it was fine. Started the engine, and tested the pedal... it almost goes to floor now.

 That is odd to loose braking because of a ABS problems. Although with codes for 2 different speed sensors, i can see happening since the ABS computer thinks those 2 wheels are at different speeds than the others so it tries to compensate. You would need to get thee ABS repair done and re-evaluate the regular brake operation, but i would think it fix that too.

So, it is possible that changing brake sensors, could fix a braking issue like this, and not it be some other type of brake issue? Since the ABS, is not the brakes?

 Yes. Two wheels fighting the other 2 wheels would cause poor braking. The pedal being low now would not be related. You may just have worn brake pads.

What do you think could make two of the sensors fail/go bad at the same time?

 Just coincidence or possibly one of the sensors codes did not turn on the ABS. Some codes come and go so fast, the light does not come on, but the computer still stores a code. So, when another problem came up and set a light, the codes where scanned, and all codes show up, no matter when they occurred.

Oh good point. So if it were your vehicle, would you begin with replacing the pads or the sensors?

 I would get the ABS fixed first. If the computer sees different wheel speeds, it will engage ABS activation no matter how hard or soft you are hitting the brakes. This will give the bouncing / fighting feeling in the pedal and poor braking. Note: just because you have a code for the right front sensor does not mean for sure it is the sensor.

Well all three codes are for the right side of the truck, and two are for the front, so, it does seem logical that the issue stems from the right side... but if not the pads or the sensor(s), no leaking, what else could it mean?

 Another common problem for a front wheel speed senor is a broken wire in the small harness to that sensor.

Question:
1989 GMC Safari. I replaced brake pads this winter and it worked fine for a while than the right front caliper started to hang up. So I replaced the rotor, caliper, and pads today and the brake still hangs up. When I installed them I used new caliper bolts and lubed them so that it will continue to float I cleaned the rotor with brake clean so no grease should be holding the brake pads to the rotor. What do you think is causing that brake to hang up?

Answer:
Thanks for being so detailed. Without driving the van, sounds like you have a problem with the caliper hose. With age and mileage, the hose can become deteriorated inside and not let the fluid which is under high pressure during brake apply, return to the maser cylinder after brake release.

This will cause the caliper piston to stay partially applied. The way to check this is to have wheel off and on a jack stand. Apply brakes a few times, release pedal, break loose the hose bolt at the caliper slowly and see if fluid squirts out under pressure. Not just leaks, but squirts out. If it squirts, and the piston / caliper releases, then you need a hose, then bleed that side. You cannot tell by just looking at the hose.

Question:
I have a 2000 GMC 3500 Savanna van. We've put a master cylinder, front brakes, adjusted rear brakes, bled the abs system through the scan tool, but we still have a problem with stopping quickly. It has a good pedal, it doesn't bleed down, but when you brake it takes it too long to finally stop. Is there something I'm missing? Thanks for your response.

Answer:
Phil, I Was wondering if you replaced those parts to fix the poor braking complaint, or did this condition come after doing one of the jobs. The front rotor surface is CRITICAL to how these vans stop. Have resurfaced some and were fine, others that looked fine still would not stop right. Even had a set of aftermarket rotors do this.

Is it a vacuum booster or hydraulic. Could be a p/s pressure problem if hydraulic. Could be contaminated brake fluid or still air in system. Nothing odd comes to mind, no service bulletins.

Also suggest putting up in air and see how far pedal travels before rears start to apply. That could signal a combination valve problem- which is part of the ABS hydraulic unit.


Our Automotive Trivia Game-
Question 1 of 10 with 0 correct
???
  True   False    

Q and A Main


How Things Work


Electrical