What is the ABS Speed Sensor all about?

Most modern vehicles have anti­-lock brake systems that use sensors to detect wheel rotation rates, reporting to a computer that is able to modulate brake pressure if one or more wheels should lock during a braking operation. Usually the sensor is a Hall­effect, or so-­called reluctance component, which looks at a toothed ring (called a tone ring) that is affixed to the wheel or axle. The teeth passing by the sensor creates a wave form that can be recognized and interpreted by the ABS controller. On three-channel ABS systems (typically found on older pickups), the rear axle is monitored by one sensor while the front wheels have their own individual sensors and anti­-lock control. Four-channel systems monitor each wheel independently.

Keep in mind:

• If one or more ABS speed sensors fail, the entire system defaults to a non-­operational status, providing no anti­-lock control. The diagnostic system will reveal to the mechanic which sensors (if more than one) have failed.
• If a sensor fails, the ABS warning light will illuminate every time you start the car, and stay lit.
• If you lose ABS intervention, you may lock up the brakes in an emergency, increasing stopping distance and losing all steering ability.

How it's done:

• The vehicle is raised and supported, then the tire is removed
• The defective ABS Sensor is replaced
• The tire is reinstalled and the vehicle is lowered
• The ABS system is rechecked for any codes
• The vehicle is road tested for proper operation