DIY - Diagnose an ABS System

DIY - Diagnose an ABS System
Posted in: How To and Tips

Why Is My ABS Light On If My Brakes Are Fine?

If you see your ABS light on, your first thought will be ‘what’s wrong?’ ABS is short for ‘antilock braking system’, the anti-skid system that keeps your wheels from locking up, and when this system isn’t working properly, it triggers the ABS warning light on your dash.

When your brake system malfunctions, there are usually telltale signs: a grinding squealing noise when braking, or vibrations when you put your foot on the pedal. But what if your ABS light is on and your brakes seem fine?

If the ABS light is on but your brakes don’t have any obvious symptoms, it might not be a hardware problem. Instead, it could be a problem with the sensors, specifically your ‘wheel-speed sensors’. These sensors read how fast your wheels are rotating, and when these sensors read that your wheels are about to lock up, they tell your ABS to kick in.

Here's how you can tell if your brakes have faulty sensors.

Diagnosing Bad Wheel-Speed Sensors

One of the easiest ways for you to diagnose a bad wheel speed sensor is to hook up a scan tool to your car and see what diagnostic codes show up. If your sensors have a low or erratic signal, they’ll generate the C0050 code.

*DIY Mechanic’s Blog*: The scanner used on most cars born after the late 90s and early 2000s is called an OBDII scanner. There are many handheld versions of this and they have multiple functions that increase with the price. Or you can get a Bluetooth OBDII scanner and have info sent straight to your phone, like a boss. Every do-it-yourself wrencher should have one.

With a scan tool, you’ll be able to check each value for your wheel speed sensors while you’re driving. If you see a value that doesn’t match the other wheels, you can use that information to figure out which sensor has gone bad.

Fixing Your ABS Light

1. Check Your Sensor Wires By Removing The Wheels

Your wheel’s speed sensors are built directly into their hub. These sensors have small, pointed parts ends sticking out, and these points read your wheel’s rotation speed. There’s another part of your hub known as the ‘tone ring’, and when it’s reading vehicle speed, the sensor is watching the tone ring for information.

A sensor can’t tell how fast you’re going if it’s dirty or broken. To check for a faulty sensor, you’ll have to remove your wheel. With the wheel off, check the sensor wires for any damage. You can also check the wires with your scan tool.

2. Check Your ABS Tone Ring For Damage

If you don’t notice any problems with the sensor wires, the next place to check is the tone ring. Your tone ring can get broken or decay, which can also tamper with your sensor’s ability to read information. To get a good look at your tone ring, you may have to remove your wheel’s caliper and rotor. If you notice any damage here, the tone ring will need a complete replacement.

3. Reset Your ABS Light After Repairs

Once you’ve found the broken part and replaced it, then put everything back together, you’ll have to reset your car’s computer to turn off the ABS light. You can reset your computer by disconnecting the positive cable on your car’s battery. If the problem has been fixed, the ABS light won’t come back on.

You can also drive around with your BLUETOOTH OBDII scan tool plugged in to check your speed sensor signals.

4. Check Your ABS System For Other Causes

If you’ve fixed your sensor, but your ABS warning light is still turning on, it could be one of several problems with your ABS components like low brake fluid, a bad ABS module, or a bad hydraulic pump. It could also be a glitch in your dashboard’s bulb check that turns the ABS light on by mistake.

Check these areas and more for additional problems that could turn your warning light on.


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3 months ago
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