2017 06 28 VAR 41 - ABS Speed Sensor

ABS Speed Sensor

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 Hall Effect, 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 waveform 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.

What common symptoms indicate you may need to replace the ABS Speed Sensor?

The ABS warning light will illuminate when the car is started, and it will stay on permanently. If you test the brakes on gravel or ice, you will no longer feel or hear the ABS mechanisms kick in, and the brakes will lock up.

How important is this service?

Functional ABS is the difference between being able to simultaneously brake and steer past an obstacle, or locking up and hitting it. It’s considered important enough for insurance companies to offer discounts to owners of cars equipped with ABS systems.
With a failed speed sensor, you’re driving around with sophisticated electronic control systems, relays and sensors that could save your life. If only they worked.