Next would be to connect a scanner so you can view live data. In this case, look at the four wheel speeds. I'd expect to see they look normal until you slow down, then one of the front sensors will drop to "0" too soon. These wheel speed sensors generate their signals magnetically. Just as with generators, you need a coil of wire, a magnet, and most importantly, movement between them. GM's front wheel speed sensors are built into the wheel bearing assemblies and they develop real wimpy signals to start with, then as speed slows down, the strength of those signals becomes weaker and weaker, to the point the computer can't read one of them, then it thinks that wheel has locked up. It activates the ABS system in response when that isn't really needed.
Where the problem gets worse is the very slight play that develops in all wheel bearings is enough to increase the air gap between the sensor and the tone ring, and that further decreases the signal strength. This is so common, it can occur to a new bearing assembly in as little as 15,000 miles. The dealers' scrap metal bins are full of these bearings. They will work just fine on a car without anti-lock brakes.
Monday, January 15th, 2018 AT 4:22 PM
