ABS Sensors
What does ABS Stand For?
ABS stands for Antilock Braking System. ABS brakes are an electronically monitored brake system that detects wheel speeds and works to prevent lock up when braking and provide traction control in slippery conditions.
How does ABS work?
A computer monitors wheel speed by using ABS wheel speed sensors on each wheel, and when a lockup is detected, it will pulse the air supply to the wheel or axle experiencing the lock-up using an ABS modulator valve. The pulsing air prevents the lock-up and helps maintain control of the truck and trailer.
How do ABS wheel speed sensors work?
The ABS wheel speed sensors work by reading a toothed ring on the wheel hub called a tone ring. The ABS sensor and the ABS ring generate an electrical current that is read by the ABS ECU, and this calculates the wheel speed and monitors for traction loss events where the wheel speeds do not match. ABS sensors are a simple coiled wire, and it is easy to test them.
What are the symptoms of a bad ABS wheel speed sensor?
A bad ABS wheel speed sensor can present multiple symptoms that should be noticed by the ABS system, and the driver will be alerted by illuminating an ABS warning light on the dash of the truck or the trailer. The trailer light will be an amber forward-facing light that is visible in the driver’s mirror. Other symptoms of bad ABS wheel speed sensors include activation when no slip is occurring (false activation) or no activation when the wheels are slipping.
How do you test ABS wheel speed sensors?
Most ABS wheel speed sensors can be tested using a DMM (Digital Multi-Meter). By checking for an open, a short, or by checking the resistance of the sensor and comparing it to the manufacturer's specification. With a DMM and a few simple tests, you can determine if a sensor has failed and should be replaced. Specification for ABS sensors will depend on the manufacturer and can vary from 500-2500 ohms, so it is essential to check the service manual for the system that you have installed.