Fix Toyota ABS that goes off with no snow or ice
If your ABS system activates while slowing down, but there’s not snow or ice on the road, you may think you have a bad wheel speed sensor. You might. But you should first examine the toothed “tone” ring for chips, cracks, scratches, and even rust buildup. All vehicles using a tone ring can be sensitive to those kinds of ABS problems. But it seems Toyotas are extra sensitive.
As the tone ring turns, each tooth induces or interrupts (depending on the type of sensor used) a magnetic field or “flux”. The gap is between the sensor and the tone wheel is pretty small and any surface imperfection can cause a false read.
The ABS control unit won’t see it as a fault. It will assume that the wheel is starting to lock up and that’s why it commands a brake line pressure release. So you may not even have an ABS light on. If you see rust build up, clean it off with a wire brush. Then spray it with cleaner to remove the rust particles (or they’ll end up on the sensor face). Clean the face of the sensor too. If you see chips, you must replace the tone wheel.
© 2012 Rick Muscoplat