The place to start is by finding a mechanic with a scanner that can access the ABS Computer to read the stored diagnostic fault codes. Those will get you into the circuit or system that needs to be diagnosed.
GM has a lot of trouble with the wheel speed sensors that are built into the front wheel bearings, but I'm not sure if that problem goes back to '02 models. You need to replace the entire wheel bearing assembly to get the sensor, but the good new is that bearing is less expensive than the same exact part without the sensor. The sensor isn't what fails. The bearing develops a little play within 20,000 miles, which is normal, but it's enough to cause the signal to drop out. That makes it look like the wheel is locked up all the time.