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Why Your Car's ABS Light Is On, and What It Means

Stephen Fogel
September 17, 2018

Your anti-lock braking system (ABS) is designed to help slow or stop your vehicle if your tires lose their grip on the road when braking.

This is critically important when the road is slick with rain, snow, ice or even oil, or when you have to slam on the brakes to stop in a hurry.

The ABS does its job by automatically “pumping” the brakes many times per second in these conditions. This system has been mandated for all passenger vehicles sold in the U.S. since 2013. 

» GET IT DIAGNOSED: Find a certified shop in your area 

Why the ABS warning light comes on

The ABS has its own warning light. It is usually depicted as a circle, with “ABS” in the center, and parentheses on either side. It will be orange or yellow when lit.

abs+light+letters abs+light+symbol

Working in conjunction with your main braking system, your ABS provides you with an extra margin of safety. When a problem is detected in the system, a warning light will come on to alert you. If this light stays on after you start your vehicle, or comes on while you’re driving, you’ll want to get it checked out.

Because your ABS is a complex system that works in conjunction with your main brakes, there can be several possible reasons why the warning light can come on. Certified mechanics will have extensive experience with ABS issues, and can resolve any issues you’re having. 

Here are some common reasons why the light can come on.

You have a defective wheel speed sensor or wiring

Your ABS is controlled by a set of wheel speed sensors, located at each wheel position. These sensors provide a constant flow of information to your ABS computer about whether each wheel is rolling normally, or if it has locked up due to heavy braking and is not rotating. 

The wheel speed sensor on each locked-up wheel activates the ABS. A bad wheel speed sensor, or a fault in the wiring that connects it, will keep the proper information from getting to the ABS computer, and can cause the system to stop functioning, illuminating the warning light. 

Solution: A mechanic can diagnose a faulty sensor or wiring with a scan tool and replace the defective parts.

Your ABS computer has failed

The ABS computer in your vehicle controls the entire system. A defect in this computer can result in the entire system going offline, which will turn on the warning light.

Solution: A diagnostic scan can reveal a computer failure. The computer will need to be repaired or replaced.

You have a bad ABS power relay

Your ABS computer system requires an uninterrupted supply of power to operate correctly. A bad power relay in your vehicle’s electrical system can interrupt or cut off the power supply, triggering the warning light.

Solution: A mechanic can find this problem through diagnostics and can swap in a new power relay.

Your brake fluid level is low

Your car needs the right amount of brake fluid in order to stop. Depending on the design of your vehicle, your ABS may have its own brake fluid reservoir, in addition to the reservoir for the main brake system. If the brake fluid gets too low, it can turn on the ABS warning light.

Solution: Check your owner’s manual to see whether your vehicle has a separate ABS brake fluid reservoir. Look for instructions for checking and topping up your brake fluid. Check the fluid levels on all the reservoirs, and top up as needed with the fluid specified in the manual. 

If the ABS light goes out after you start your vehicle, and no other brake-related warning lights stay on, it should be OK to drive it. If the light stays on, call a mechanic.

» LEARN MORE: How to bleed your brakes

Get it diagnosed by a professional
 

Can I drive with the ABS warning light on?

If the ABS light comes on while you’re driving, and no red brake warning lights are illuminated, don't panic. Find a safe place to pull over, turn your vehicle off, and then restart it. If a fluke in the ABS system triggered the warning light, it should turn stay off when you restart the engine. If it comes back on, it's likely time to call a mechanic and get an ABS system diagnosis. Until it’s fixed, drive gently and avoid hard braking that could provoke a skid.

If the ABS warning light and the red main brake warning light both come on, you should not drive your vehicle until the problem has been fixed. It is simply too dangerous to do so. Your entire braking system is affected, and may not be able to stop your vehicle the next time you apply the brakes. Have your vehicle towed to a mechanic for repairs. 

 

Stephen Fogel

About the Author

Stephen has been an automotive enthusiast since childhood, owning some of his vehicles for as long as 40 years, and has raced open-wheel formula cars. He follows and writes about the global automotive industry, with an eye on the latest vehicle technologies.

1 User Comment

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By , March 01, 2018
I was hopin to find somethin on Toyota 4runner VSC Trac light on. I have a ‘03 4runner with VSC Trac and ABS lights on. I did the zero point calibration properly and as instructed, the lights flashed but came back on. If anyone has any idea what to do, i will appreciate it.