Anti Lock System Testing and ABS Repair
Got an anti lock warning light on? We are a team of ASE certified mechanics
who have created this guide to help you fix a problem with your ABS system yourself and save a considerable amount of money in the process.
Or at least see what you are paying for when having it repaired. ABS stands for
“anti-lock brake skid” safety control system. Let’s jump right in.
In This Guide
- Before you begin
- Anti lock warning light is on?
- Fuse location and test
- Wheel sensor testing
- Wheel speed sensor replacement
- Anti lock system computer module replacement
The anti lock skid control system is designed to keep you car under control
in a hard braking event. When one or more tires begin to skid they loose
traction to the road allowing the vehicle to go in whatever direction is wants
and even completely sideways. Research has shown that a vehicle with an anti-lock
system can decrease the chance of a vehicle accident by 18%.
Though early designs were comprises of many parts today’s systems are much
more basic to include a main computer or module, a valve and hydraulic pump
assembly and four wheel speed sensors, one at each wheel. This simplifies
repairs and brings the cost of the parts down.
Wheel speed sensors are located near the wheel and monitor the rotation
speed. Then this information is sent to the computer module which computes data
from all four wheel sensors. If the computer see’s one or more of the wheel turning
slower than the others it signals the valve and pump to dump brake line pressure
to allow the wheel or wheels to start rolling again. The pump portion of the system
maintains the pressure once the wheel regains speed. This is why you will feel
the brake pedal vibrate when the system is activated which is normal.
When the ABS system detects a problem, a fault code is stored in the system
control memory and illuminates the warning light. Most ABS systems are
“real time”, so when a code has triggered and then repaired the code
should clear itself within a few minutes of driving.
Before You Begin
Start once you have determined you are going to fix the problem, park the car
on level ground with the transmission in park and the emergency brake set and
the engine turned off.
You may need to jack the car up to remove a tire or replace a control module
and we prefer you learn how to do it correctly so you stay safe.
to use a floor jack and stands
Through this guide you may need to remove a tire for testing
and part replacement purposes.
How to remove and reinstall a wheel
The brake caliper and brake pads may also need to be removed when replacing a
wheel speed sensor.
How to remove a brake caliper and pads
The tools, equipment and supplies seen in the article along with additional
information using specific repair manuals are available at the end of this
Anti Lock Skid Warning Light
When this warning light flashes or stays on steadily it means the system is
disabled. So if you are in a situation where the car needs this safety system it will not work and you could
lose control of the vehicle. In the following guide we will show you the first
things to look for when this light comes on and how to repair the system. An anti
lock warning light will be in different places in the instrument cluster for
each car, and it maybe accompanied by a red warning light.
Here is a video that will show you what you are in for so you can feel more
comfortable about the repair. Once you have watched the video continue down the
guide for more detailed information which is updated regularly. We will present the easiest things to check first before heading to the more complicated
stuff. Let’s get started.
There are two ways to go about this repair. Either you can purchase a code reader capable of reading ABS codes from about $44.00 from
Amazon or you can start checking the system manually.
Most ABS diagnostic codes can be accessed by the ALDL
connector much like the
engine computer control system.
How to Test an Anti-Lock System Fuse
When you see an ABS warning light the first thing you should check is the
system fuse, this is done by the use of a simple test light. The abs system is like any other electrical system and is protected by a fuse
that can blow if an electrical surge or short circuit occurs or if the fuse ages.
When a short circuit occurs there is usually a problem in the ABS pump motor or controller. Most ABS fuses are located
in the fuse panel under the dash or in the power distribution center under the hood.
Consult your car’s owner manual for exact locations and follow the guide below.
Here is a video that gives you an idea on how to locate and test the
fuse. Once you are done watching continue down the guide to get more information
and tips on the repair.
Step 1: Locate Fuse
Locate the fuse panel or power distribution center either under the hood or dash depending on
the manufacturer and model of your car. If you cannot find the ABS fuse location consult your owner’s manual or you can check an online manual like
When checking this fuse look for corrosion or rust and see if the fuse is loose or melted.
These are all signs the fuse is having a problem. Then
connect the test light to ground
so you can be ready for the test. This
test light checks continuity of the fuse and if power is present at the system. Also
check for corrosion and water in the power distribution center, dry or clean as necessary. Try to
wiggle the fuse to see if it’s loose, if so use a small standard screwdriver to
enhance the connection by bending the metal terminal prongs inward to enhance
On the bottom of the fuse panel lid there is usually a diagram showing the
identification number of the fuse and the amperage used.
There should be a “road map” showing the location of the fuse on the same
panel. Here is the diagram that shows you where the fuse is located in the panel
that correlates with the identification number. Some fuse panels only have
a number location in which case the owners manual must be used for this identification.
Step 2: Test and Replace Fuse
Once located, use a test light which is connected to ground to test both sides of the
fuse. This will ensure the fuse is working correctly. If you cannot seem to get
power at either side of the fuse touch the test light tip against the positive
side of the battery, it should light up. This will let you know the test light
is working. The ABS system relay is integrated into the unit on some cars while
other models will have the relay in the same panel as the fuse. If so, this relay should be checked and replaced if it is not working.
How to Use a Test Light and
How to Test a Relay
If a blown fuse is found, replace it with a new fuse of the same amperage.
Never install a fuse with more amperage than is called for as this could cause damage to the
wiring or additional components.