You need a mechanic with a scanner that can access the Anti-Lock Brake Computer to see what the system is reacting to. GM has a real common problem with the front wheel bearings developing enough play to let the wheel speed sensor's signals drop out, especially at lower speeds when those signals are normally weakest anyway. That play in the bearings is normal but due to their design, the wheel speed sensors can't tolerate any increase in the air gap because those signals aren't very substantial to begin with.
When a signal drops out, it typically causes false, or unnecessary ABS activation when coming to a stop because the computer thinks that wheel stopped turning. It can also cause the traction control system to activate because one wheel is turning faster, (it thinks), than the one with the missing signal.
If the live data on the scanner does show a signal dropping to 0 mph intermittently, the fix is to replace that wheel bearing assembly. The dealer's scrap metal bin is full of them. The play that develops and causes a problem can occur in as little as 15,000 miles.
Be aware too that ABS Computers will set diagnostic fault codes in memory and turn on the yellow warning light if a wheel speed signal goes missing long enough, but many of those computers can only store one wheel speed sensor code at a time. They will not have anything accurate then to compare the other wheels to so even if a second sensor fails, no second code will be set. It WILL set after the first problem is fixed and that code is erased. What that means is your mechanic can use his scanner to read the stored fault codes and find only the one, give you an estimate for a new wheel bearing, replace it, THEN the new code finally sets and he has to tell you there's more wrong with the system. They hate having to do that but there's no way to know about the second problem until the first one is fixed. That happens more often when you let the first problem go for many months. That give the other parts a lot of time to fail. That happens a lot on GM front-wheel-drive cars too because the sensors stop working at such low miles.
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Wednesday, May 9th, 2012 AT 7:32 AM