ABS light comes on

Tiny
GOBLUE1878
  • MEMBER
  • 2003 PONTIAC GRAND PRIX
  • 150,000 MILES
I just had a brake system flush two weeks ago now the ABS light and traction control light comes on when I push the brakes. Whats going on and how do I fix it?
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Thursday, May 2nd, 2013 AT 5:06 PM

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Tiny
CARADIODOC
  • EXPERT
This has been a really big problem for GM front-wheel-drive cars and it likely had nothing to do with the recent service. Due to their poor design the wheel speed sensors develop really wimpy signals to start with, especially at low speeds. Play develops in the wheel bearings that is perfectly normal, but with this design it lets the signals get even weaker, to the point a signal may drop out making it look like that wheel is locking up. This commonly happens in as little as 15,000 miles. A new bearing assembly will solve the problem but it is likely to occur again in as little as another 15,000 miles. The dealers' scrap metal bins are full of these bearings.

The typical symptom is false activation at low speeds when the tires are not skidding. The warning lights will be turned on when the missing signal is detected when the brakes are not applied. You described it a little differently so there may be something else going on. There will be a diagnostic fault code stored in the ABS Computer that will lead you to the circuit or system that needs further diagnosis. The cause could be as simple as low fluid level in the reservoir. If it is low, just add a little fresh, clean fluid. Don't fill it. There is either a leak or the front disc brakes likely need to be replaced.

Along with the wheel bearing issue, be aware that if you ignore that long enough, a second problem could develop, as in the other bearing getting sloppy. The computer compares the wheel speeds to each other and when a fault code is set of one, it knows it can't use that as a reference so it won't run the self-tests on the others, therefore it won't set a second fault code. (A missing signal code is different than a code related to the electrical wiring. That can still be detected). All your mechanic will know from reading the codes is that one signal is missing and that one bearing needs to be replaced. It's not until that is done and he is out on the test-drive that the self-tests will resume running and the second missing signal will be detected. The yellow warning light will turn on again and he will have to start his diagnosis all over. That's very frustrating for mechanics who hate having to tell you more parts and services are needed, and it's frustrating for owners who incorrectly think the mechanic diagnosed the problem incorrectly. Most of that frustration can be avoided if the problem is diagnosed and repaired right away before that next problem has a chance to occur. Often that second problem isn't detected right away. It's not uncommon for it to show up a day to a week after the previous service.
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Thursday, May 2nd, 2013 AT 5:43 PM

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