The common problem on GMs with removable sensors is rust builds up under them and pushes them up. That increases the air gap and decreases the signal strength. These sensors develop rather wimpy signals to begin with, so a decrease is exaggerated when the vehicle slows down. Movement between parts is one of the three ingredients in generating a voltage, and as speed of that movement slows down, the signal being generated gets weaker, until it reaches the point where the computer can't read it and it thinks that wheel has locked up.
The clues here are generally the faults will be detected at slower speeds. The anti-lock system will only activate when the brake pedal is pressed, and you usually don't do that for very long at higher speeds. The traction control part of the system activates during acceleration. A signal dropout during braking or accelerating will activate the appropriate system, but when you're cruising at a steady speed, a dropout is detected as a defect, and that's when the diagnostic fault code is set and the warning lights turn on.
You didn't indicate that you actually had the fault codes read and recorded, so you're just going by what other misinformed people thought fixed the problem. It's important to understand that when the warning lights turn on, there is a diagnostic fault code to tell you which circuit or system needs further diagnosis. Even with wheel speed sensors, there are multiple fault codes that can be set and they mean very different things and have different repair procedures. A code can relate to a break in the electrical circuit to a sensor. A common cause of that is corrosion buildup between the mating terminals in a connector. Replacing the sensor can make the problem appear to be fixed due to scratching action of sliding the connector together. That scratching creates clean and shiny spots for the terminals, but the corrosion always comes back weeks or months later.
A speed error code related to a speed sensor is often due to a cracked tone wheel, but a tire of the wrong circumference will do that too. A sensor's signal can be missing, as I first mentioned, but electrically the circuit is still intact. That will set yet a different fault code.
Thursday, November 5th, 2015 AT 1:52 PM