All ABS-equipped vehicles
Vehicle had wheel bearing hub replaced on one side.
If you diagnose a bad hub bearing on one side of a vehicle, and the ABS wheel speed sensor or tone ring is integral to the bearing, you may need additional repairs to restore proper ABS functioning.
In many cases, replacing one hub bearing will cause the driver to feel ABS false activation when coming to a slow stop on dry pavement. False activation is usually described as a pulse in the brake pedal when not expected. The pulsation comes from the ABS valves cycling the supposedly locked-up wheel. This is due to the difference in signal strength from the wheel speed sensors (WSS) side to side. The problem is usually associated with air gap difference or wiring and/or connector integrity. In many cases, removing the WSS from the other side, if possible, and cleaning the mounting surface may repair the problem. The rust build-up actually lifts the WSS from the bearing, increasing the air gap and weakening the signal.
Another possible issue is play in the bearing causing sine wave frequency change and/or AC voltage variation. The new bearing will have little to no play, and the remaining hub will have acceptable play, but can still affect signal strength.
Again, the difference in signal from side to side may be enough to trigger false activation. If WSS are integral and not serviceable, replacing the hub bearings in pairs may be the only answer. In these cases, the ABS system is activating as designed, so no warning light will be illuminated most times. Discuss this with the customer to prevent surprises in the future and the dreaded, “It never did this before you worked on it” conversation.
Courtesy of Raybestos.