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On many outer constant velocity (CV) joints is a reluctor or tone ring.
As the windows or teeth pass by the wheel speed sensor (WSS) in the knuckle it creates or changes a signal that is interpreted by the ABS modulator as the speed of the wheel. If the ring is out of alignment on an outer CV joint, it can cause WSS codes and the ABS to deactivate. Andrew Markel discusses how to inspect the outer CV joint and attached tone ring. This video is sponsored by GSP North America.