A bad wheel speed sensor can cause and ABS or traction control warning light as well as causing some speedometer issues.

This ABS sensor mounts to the rear axle hub mount and reads the speed of the hub as it turns. When working properly it will react with the ABS system to pulsate the wheel according to braking hence, being able to steer under extreme braking conditions. If you have the ABS light on or any malfunction this could be your problem.