What you're describing involves two totally different systems. Speed sensors on a part of the drive train are for shifting and the speedometer. The anti-lock brake system uses a wheel speed sensor at each front wheel, and to save money, GM usually uses just one sensor in the rear to measure both rear wheel speeds together. Unless something has changed, that one sits on top of the differential housing. They did have some older models that used the speed sensor at the rear of the transmission for the anti-lock brake system.
The place to start is not by replacing random parts. Start by reading the diagnostic fault codes, but understand those never say to replace parts. They only indicate the circuit or system that needs further diagnosis, or they describe the unacceptable operating condition. A part referenced in a fault code is only the cause of that code about half of the time. You also have to look at the wiring and connectors.
Most likely you'll have to visit a mechanic to have ABS codes read. Many auto parts stores will read codes for you for free, but they can only read engine codes.
Wednesday, February 13th, 2019 AT 7:26 PM