Symptoms of a Bad or Failing ABS Control Module

All modern vehicles are equipped with an antilock brake system (ABS). The technology regulates brake fluid pressure to prevent wheel lockup during a panic stop or when stopping on slick surfaces.

A computer, called the ABS control module, is the heart of the ABS system. Although module failure is rather uncommon, it can happen, often resulting in one or more troublesome symptoms that you’ll want to address right away.

What is an ABS Module?

The ABS control module is a microprocessor that runs diagnostic checks of a vehicle’s antilock braking system and processes information from wheel-speed sensors and the hydraulic brake system to determine when to release braking pressure at a wheel that’s about to lock up and start skidding.

Antilock brakes have been available since the 1980s and are standard on all 2012 model-year and later vehicles because they’re an integral part of electronic stability control, which has been required since 2012.

Antilock systems prevent skids when braking and stability control intervenes to prevent skids even when the brakes aren’t applied.

A dashboard ABS warning light is supposed to come on for a few seconds every time a vehicle is started, but if it comes on while driving it signals that the control module has conked out, a wheel sensor has failed or another problem has developed.

Symptoms of a Bad ABS Control Module

Symptoms of a Bad ABS Control Module

Here are the obvious signs that can help you detect an ABS control module issue:

#1. The ABS Warning Light Glows.

This is the most common sign of problems with the ABS system. Just be aware that the dashboard ABS warning light is supposed to come on for a few seconds when you start a vehicle, so don’t panic.

If the ABS light remains glowing, try turning the ignition key off and back on, like rebooting your computer. Some transient issues may confuse the ABS control module, and restarting the car could help clear that.

If restarting doesn’t make the ABS light go away, it’s probably time to call your mechanic. The ABS light triggers a code that helps your mechanic pinpoint which ABS component is causing the problem.

If you’re driving and the ABS light suddenly glows, this can indicate a failure with one of the ABS system components, including the ABS control module.

Again, don’t panic.

Some components of the anti-lock brake system may still function despite the glowing ABS light. The anti-lock may not work, and stability control and traction control might also be disabled, but as long as your conventional brakes aren’t compromised, you should still be able to brake your car just fine.

Keep in mind that select vehicle groups (older cars) equipped with earlier ABS systems might not have an ABS light. These use the Check Engine Light instead.

#2. The Brakes Lock Up.

The ABS system prevents any wheel from locking up during heavy braking. So, when an ABS control module fails, you’ll likely notice it when applying more braking pressure.  

A bad ABS module can behave erratically, making your brakes lock up even under normal braking. You might even notice unusual behavior from the brakes, like random clicking noises. These can also indicate ABS module failure.

Here’s something to note — if one tire is consistently locked, it might not be the vehicle ABS but a stuck caliper instead.

#3. An Unresponsive Brake Pedal.

Your brake pedal may slowly become unresponsive over time.

At first, you’ll have to press the pedal a couple of times to get some braking action.

Eventually, you’ll have to press down multiple times to get it to work, indicating a deteriorating ABS module.

However, an unresponsive brake pedal can mean many other things. Have your mechanic check the brake fluid level and flush the brake system, so there’s no air in the brake lines.

#4. Increased Pedal Effort.

The symptoms of a bad ABS module include spongy brake pedals as well. This happens if the brake fluid drops below the required level in the reservoir or due to a faulty ABS control module.

The ABS control module pumps extra brake fluid into the brakes when required. The faster the brake pedal is pressed, the more fluid is pumped into the brake line until are reach the full brake pressure without wheel locking.

During this period, if you experience spongy brake pedals, it is because your brakes received an increased brake fluid from the ABS unit. An unresponsive brake pedal must not be taken lightly.

#5. Speedometer Failure.

There are rare cases where an ABS control module failure affects the speedometer. It’ll either show you the wrong speed, or the needle will rest at 0 mph.

Next, the brake light or Check Engine Light will likely switch on. Even if those lights don’t come on, a faulty speedometer is a reasonable cause to have your car checked out.

What Causes an ABS Module to Fail?

The ABS module can fail Rarely due to moisture, corrosion, and other external factors. It is often one or more sensors, or the wiring to the sensors. Software glitches and normal wear can also lead to a module that needs to be reprogrammed or replaced.

Malfunctions also occur when sensor wiring becomes damaged, resulting in intermittent or no continuity. In more corrosive environments or serious brake system neglect, brake fluid can become contaminated and the hydraulic control unit fails to function.

If you have a malfunction in the ABS, physically check all wiring and the brake sensors first. When checking the brake sensors, look for metal shavings and other debris that could cause false feedback to the electronic ABS controller. False feedback causes the ABS to trigger when it shouldn’t, or not function when it should.

You may not have an ABS scan tool at home, but any reputable repair shop will have one, and the scan tool is invaluable if you can’t find a physical reason for your ABS issues. After the scan tool produces a fault code, you can proceed with your ABS troubleshooting. Whatever the problem, the repair is much easier once a fault is established.