abs problem

[tazzen]

this is actually about my wife's truck (GMC, 97, 1500, 4x4, 5. 7, auto, ext cab). it has approx. 56k miles on it. the problem is, when she is in the final stages of stopping, her brakes will give a quick release like she is starting slide but it only releases once and grabs right away. sometimes it will do a little more where it lurches forward 6". we have taken it to several garages and they cant find what it is. we have had a scan tool hooked up and they say it happens too fast to show a code. can anybody help us with this or any suggestions (other than a new ctd for the wife) or even a possible GMC site that is as well educated as TDR. also the wheel sensors have been checked on all 4 wheels and that came up empty handed.





P. S. there is a CTD in the future for her, if she can behave herself, but now we need to fix the gmc problem.

 

[Cumminpwr11]

my 99 does the same thing. hopefully you find something. 5 different brake shops couldnt find a thing. a was almost begging for them to take my money didnt care how much just fix it. they couldnt find a thing



good luck





Chris

 

[tazzen]

thanks for your help chris. i just got back from the dealer and they were able to get a code but dont know yet if that is the problem. they said it could possibly be ebcm so now we will have to try that route. we will let you know if that is what comes out of it



thanks

ed

 

[Bigramguy]

Check the front tone rings for the ABS,they may be cracked. We have seen a lot of these lately with the same style problem. It will rarely show up on the scan tool. Clean them down good with a toothbrush and some brake cleaner and look for little hairline cracks,they will be small but noticible. If there are any,replace them and try it before you replace the ECM. Not much ever goes wrong with the ECM,9 times out of 10 they are incorrectly replaced. While your in there clean off the sensor heads as well,as sometimes they will pick up metal shavings and act up.



Make sure you have eliminated everything else first. Try disabling the ABS and see if it still does it. If it does then it is probably a mechanical problem.

 

[wtrenholm]

Chris,



The GM Tech 2 (GM's scan tool) has a snapshot feature that basically takes a movie of data over a short period of time. The tech should be able to take a snapshot when the problem is actually happening and then review it frame by frame to watch if the ABS was indeed activated and also look at each wheel speed sensor frame by frame to look for issues. Also Kelsey Hayes ABS runs the pump anytime the ABS is active, so if you hear the pump running the controller is definately getting bogus info.



Big ram guy is right that the tonewheels can crack. A few I've worked on have caused false ABS activity just before coming to a stop.



Good luck,

Wayne