ABS light on: What it means and how to fix it

Learn what an ABS light means and what to do about it

The anti-lock brake system (ABS) is a critical safety feature in modern vehicles. It prevents the wheels from locking up during braking, thereby maintaining traction and steering control. When the ABS light illuminates on your dashboard, it indicates an issue with the system, and a trouble code is stored. Addressing this issue promptly is essential for your safety and the proper functioning of your vehicle. A Traction Control System (TCS) is another crucial safety system that works with the ABS to enhance vehicle stability and control, especially in slippery conditions. Here’s a guide on how to fix and reset an ABS light and a traction control light.

The most common causes of an ABS light or TCS light

Since both the ABS and TCS systems rely on input from the wheel speed sensors, yaw sensor, lateral acceleration sensor, and steering angle sensor, sensor failure or sensor wiring harness issues are the most common causes for ABS or TCS trouble codes, and an ABS or TCS warning icon on your dash.

The wheel speed sensors fail most often. They’re exposed to the elements, and the tone rings can accumulate rust and debris. In addition, repair work on the brakes, wheel bearings, etc., can disturb the ABS sensor wiring harness, causing a fault code to set.

What to do when you see an ABS or TCS light on

An ABS or TCS warning icon means the system has detected a fault and disabled the ABS and TCS systems. You can continue to drive the vehicle, but you will no longer have anti-lock braking or traction control. However, the brakes will continue to function.

Get the ABS or TCS trouble codes read. That will tell you which component is causing the problem. Then, troubleshoot the component and fix it. The ABS light will continue to light unless you fix the problem.

How to reset an ABS light or TCS warning light

The ABS system constantly monitors the status of the ABS control module and wheel speed sensors. You can clear an ABS or TCS code using an inexpensive code reader. However, unless you fix the underlying problem, the ABS or TCS warning light will reappear as soon as the ABS control module detects the fault, which usually happens as soon as you start driving again.

If you’ve fixed the problem, simply connect your code reader or scan tool and select CLEAR CODES. Then start the engine and drive. If the problem has been fixed, the ABS light and TCS light won’t illuminate.

Understanding the role of the three major components of an ABS system

Wheel speed sensors— These sensors monitor the rotational speed

Wheel speed sensor

of each wheel and send this information to the ABS control module. Over the years, carmakers have used two types of wheel speed sensors: active and passive. Here’s a short description of both types.

Magnetic Inductive Sensors (Passive Sensors)— These sensors use a toothed wheel (tone ring) that passes by a magnetic sensor. The sensor creates an analog AC sine-wave
voltage as each tooth passes the sensor.

Hall Effect Sensors (Active Sensors): These sensors use the Hall effect principle to detect changes in magnetic fields caused by the passing of a toothed wheel or a multipole magnetic ring. They require an external power source and produce a digital signal.

For more information on how wheel speed sensors work and fail, see this article

ABS hydraulic Unit— The ABS hydraulic unit consists of a pump,

This image shows a typical ABS hydraulic control unit with a pump, motor and valve assembly. The unit on the right is the ABS control module

with multiple valves, an accumulator, and a motor. The valves open and close based on commands from the ABS control module to bleed hydraulic pressure to a skidding wheel and then close to rebuilt pressure. The motor and pump build the hydraulic pressure to dump and then rapidly rebuild pressure to the skidding wheel.

ABS control module— The ABS control module receives input from each wheel speed sensor and determines if the vehicle is about to lose friction with the road. At that point, the module commands a rapid sequence of dumping and reestablishing pressure to the locking wheel.

The major components of a Traction Control System

The complete ABS system— The traction control system works with the ABS system, so it uses all the ABS sensors, valves, and the control module.

Yaw Rate Sensor— The yaw rate sensor detects changes in the

A steering angle sensor is mounted near the bottom of the steering column and reports the driver’s intended path to the traction control and stability control systems

vehicle’s rotation around its vertical axis during brake applications.

Steering Angle Sensor— The steering angle sensor monitors the driver’s intended path

Throttle Position Sensor— The throttle position sensor monitors the driver’s intended acceleration

©, 2014 Rick Muscoplat