Once the light comes on there is a diagnostic fault code stored in the computer. How can they say nothing's wrong when they have a code to look at? The most common problem on GM front-wheel-drive cars has been the front wheel bearings. They are not defective or worn out, but they develop enough normal play that the signals drop out from the wheel speed sensors. That makes it look to the computer like that wheel is locking up. GM likes to build those sensors into the bearing assemblies so you have to buy more parts. Funny thing is that bearing is less expensive with the sensor than the exact same bearing without the sensor.
Another common problem occurs if you let this one go for a while. A second problem can develop, typically the other wheel bearing, but it won't set its own fault code because with the first code already set, the computer can't use that erroneous signal to compare other wheel speeds to it. That causes the light to turn on and the new code to set right after having the first problem fixed. A lot of people blame the mechanic for not diagnosing or fixing the problem correctly when the real cause was two different problems but only one set a fault code.
Sunday, July 24th, 2011 AT 6:55 PM