Anti-Lock Brakes Explained

By Brian Klaubert

This past month I bought a used pick-up truck. It had some major work that needed to be done before it was drivable, but it also had the ABS warning light on. ABS stands for “Anti-lock Braking System”. The major repair work was done quickly enough, but the ABS light had to wait until calmer times. I drove the pick-up for two weeks without anti-lock brakes.

I was suddenly reminded of what a great feature anti-lock brakes really are. I have been driving with anti-lock brakes since 1992. All of a sudden, when braking for a yellow light, or quickly decelerating for a side street I almost drove past, my back wheels were skidding. This caused a lot of concern for me, the drivers around me, and for my kids in the truck with me.

Stop and think about it. You almost never hear tires skidding anymore. That’s because these days almost every vehicle has some form of anti-lock brakes.

There are three primary components to any anti-lock braking system. There are sensors that constantly measure the rotational speed of each tire, there is an actuator – the device that provides the anti-lock function, and a computer that monitors and controls everything.

Your ABS warning light is an indication that some part of the ABS system is not working. It does not mean that your brakes are not working. Your brakes will work like brakes have always worked. But you will not have the additional safety of the anti-lock, or anti-skid, system. This does mean that under many heavy braking situations your car will travel farther before coming to a stop.

Fortunately, when your ABS light comes on, it is usually just a sensor that has gone bad. The sensors are the least expensive components to replace in the system. I would estimate that in 80%-90% of the instances of an ABS light being on, the problem is a sensor.

If the problem is with the ABS actuator, the repair will be very costly. An ABS actuator is usually more than $1,000 to replace. Typically, less than 10% of the problems require replacement of the actuator. However, the people that have had to replace the actuator scare everyone else who has the ABS light come on.

So, what about my truck, how much did that repair cost? The problem was a wheel speed sensor. The retail cost of the repair, including part, labor and the diagnostic charge, was $165.

Proper maintenance of your vehicle will prolong the life of your ABS system. Many manufacturers are now recommending flushing your brake hydraulic system every 30,000 miles. The reasons are two-fold. First, braking generates a lot of heat. The heat oxidizes the brake fluid, and oxidized fluid allows more wear of the actuator components. Secondly, brake fluid absorbs moisture. Moisture can create corrosion in the ABS actuator.

Proper procedure when performing a brake pad replacement is to bleed the oxidized fluid from the brake caliper rather than push it back up into the actuator system. Unfortunately this takes a little extra time and many repair facilities do not do it.

Lastly, bleeding or flushing the brake system on a vehicle with ABS is not like bleeding the brakes on your father’s Oldsmobile. Many cars require an expensive diagnostic computer to exercise the ABS actuator when bleeding the brakes. The ABS system is truly no place for a weekend warrior to be tinkering. The potential repair costs are great.

Brian Klaubert owns Christian Brothers Automotive – Hamilton Mill, on Hwy 124 in Dacula.