You probably know the Check Engine light means something is up with your vehicle’s engine. A light illuminating the dash could mean you need an oil change or even a new engine. An ABS light is different because it only relates to your braking system. This could be a simple fix or a complex issue. What does ABS mean? How does the ABS system work? How much downtime and expense does getting the ABS light to go off involve? Here’s what to know.
What does ABS mean?
ABS is an acronym for anti-lock braking system, an anti-skid sub-component of the braking system. As the name suggests, it means the brakes do not “lock up” no matter how hard you step on the brake pedal.
Back in the days of carburetors, bias-ply tires and AM-only radios, your average car didn’t have ABS. In older cars without ABS technology, stepping on the brake pedal drives a piston in the brake caliper to push the brake pads against the brake rotor. Stomp on the pedal too hard and the friction force locks up the rotor, causing the wheel to freeze in place. Experienced drivers were taught to pump the brakes rather than slam them to avoid locking them up. That works, but it’s not ideal in a stressful emergency situation.
While the aviation industry used ABS systems for years, engineers were slow to add the expensive tech to street vehicles. A few expensive motorcycles and cars like the Jensen FF started using ABS as early as 1966, it wasn’t until a 1971 Fiat patent for a modern, simple and efficient ABS system that manufacturers started offering ABS in large numbers.
Originally for luxury cars like the Lincoln Continental and Chrysler Imperial, manufacturing costs lowered with mass production and ABS became optional in mainstream cars like the Toyota Camry by the late 1980s. It took another 30-plus years before ABS was required as standard equipment in 2013.
An ABS car works much the same way as a non-ABS car, only with the addition of a few components such as wheel sensors and an ABS controller. This system uses wheel speed sensors to “see” when the wheels are about to lock up while the car is moving. The controller sends a signal to release some brake fluid and pulse the pressure going to the pad, letting the brake rotor slip and the tire regain grip.
This happens 20 times per second, preventing a dangerous loss of traction. The result is reduced braking distances and the ability to steer during the even hardest braking. The downside is when something goes wrong, you’ll be introduced to the ABS light.
What does the ABS light mean?
An illuminated ABS light doesn’t mean your brakes aren’t functioning. Instead it is an indicator that some part of the ABS system has an issue and might not be working properly. Just as you can run the engine with the Check Engine light on, you can still drive and brake with the ABS light on. It just means your vehicle’s brakes might be operating as non-ABS brakes.
You might notice the ABS light illuminates right when you step on the brake. This is because the ABS system usually only monitors for wheel slip when the brakes are activated. A brake pedal switch is an open circuit until you press the brake pedal. This closes the circuit, illuminating the brake lights and powering the ABS relay to take readings from the wheel sensors.
The ABS system has a self-test that performs a function check at every startup. Like the rest of your instrument cluster lights that go out after a few seconds, the ABS light turns off when everything checks out as good to go. If the light stays on, some part of the ABS system has failed or has a communication error and you’ll see an ABS light. Here’s how that happens.
Reasons for the ABS light
Let’s look at what could have gone wrong in your vehicle. It’s usually one of a handful of causes.
Damaged/disabled wheel speed sensor
Vehicle speed sensors use a rotating reluctor wheel and fixed magnet to generate a signal to send to the ABS module so it can calculate wheel speed in relation to vehicle speed. Both are tough components, but they can fail. A damaged or disconnected sensor will let you know through the ABS light.
Bad ABS module
An ABS module is the microprocessor or computer behind the ABS programming. Just as the engine has a computer in the electronic control unit, the ABS system has one with the ABS module. This system receives input from wheel sensors and processes data to make decisions on which brakes to operate. It also stores malfunction codes and other information and sends output signals to the solenoid valves that modulate the pressure on the braking components. The output signal from the ABS module is also what ends up physically activating the ABS light.
Hopefully this is your issue, because it’s an easy diagnosis and fuses are cheap to replace. A blown fuse creates an open circuit that disables ABS components because they don’t receive power. Before swapping out difficult to reach components, look at the fuses. ABS fuses are often in the vehicle’s main fuse panel.
Low ABS fluid
The ABS system relies on the proper amount of brake fluid in the system in order to work. The control of that fluid is the basis for how ABS, as well as the rest of the braking system, works. Low brake fluid can cause an ABS light, but you’ll probably notice other symptoms, such as a soft, spongy-feeling brake pedal.
Every vehicle will start to wear out as the years and miles add up, and that includes electrical components. Wires can take damage from fender benders and road debris, rodents and improper repairs or just corroding and oxidizing. Broken wiring interrupts the signal between the wheel sensor and the ABS controller, and that missing information is enough to send up the ABS light.
The system is turned off
If you’re a professional racing or stunt driver (or bought your car from one) and have the experience to control the brakes better than the computer, the ABS braking was likely turned off for improved driver control. For normal drivers, however, there’s never a good reason to turn off ABS.
Turning off ABS could be a setting buried in the infotainment screen’s vehicle settings, or it could be as simple as unplugging the ABS relay or fuse. The ABS system can also be turned off by a mechanic putting it in maintenance mode as part of a troubleshooting procedure to narrow down component failure between the ABS and stability control systems.
Traction control problems
The stability control, or traction control system, uses the same wheel speed sensors and other ABS components to perform its safety monitoring and tasks. A failed traction control module will likely cause an ABS light because failures in the associated components disable the ABS system.
What to do if your ABS light comes on
Keep in mind, the yellow ABS light comes on or flashes during ABS operation, so if you intermittently see it during hard braking, odds are the system is fine. But let’s say your ABS light is on steadily and you think it’s a malfunction. There are some steps you can take to get the underlying issue resolved. If you have a code reader with the ability to scan ABS subsystems, use that to narrow down the likely culprit. If you don’t have a code reader, one with ABS scanning ability is a bit more expensive, starting around $100.
With the code to narrow down the issues, you’ll know to replace the wheel speed sensor or the specific component giving you trouble. Speed sensors average $50, while an AMS module is quite a bit more complex and will cost a few hundred dollars.
Not into DIY? That’s fine, just get your vehicle to the dealership or your local mechanic as soon as possible. ABS is a handy safety feature, so you don’t want to drive without it for too long. If it’s a long way until payday, you can still drive your vehicle with an ABS light illuminated, but keep your distance from other vehicles and brake early. A disabled ABS also can interfere with stability (traction) control, so hit up your mechanic as soon as you can.