GM has a huge problem with wheel bearings with the sensors built in. They develop normal play but that is enough to allow the signals to drop out intermittently. The clue is the warning light will not turn on as soon as you start the engine, (after the six second bulb test), because during the self tests, the electrical continuity of the sensors are fine. While moving, the computer sees the missing signal from one wheel while it sees good signals from the other wheels. Note too that the ABS Computer compares the two front wheel speeds to each other. When a code sets for one of them, it won't set a code for the other one. That means if you have a code for the left front wheel and you replace that bearing, you might have the light come on again right after that service and the code will be for the right front wheel. The dealer's junk metal bins are full of these bearing assemblies but if you get your old ones back, they can be used on cars without anti-lock brakes. The same bearing without the sensor actually cost almost twice as much as the bearings with the sensor, and they're the same part. Of course there are other possible causes for the light to be on. Having the stored diagnostic fault code read is the place to start.
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Tuesday, March 22nd, 2011 AT 6:57 AM