If you are getting an "ABS" or "Brake" light on your vehicle, there is a chance that your ABS wheel speed sensor is not functioning properly.
Note: A vehicle service manual for your vehicle should explain the exact procedures for removing the sensor.
ABS Sensor Test
Step 1- Remove the ABS sensor from the vehicle.
Most sensors are mounted directly into the top or side of the rear end (pumpkin), and are only attached by one or two bolts. Once the bolt(s) is removed, disconnect the electrical connector from the sensor housing.
Note: Some vehicles use two separate ABS sensors with one on the front differential, and the other on the rear differential. This is common on 4-wheel drive vehicles. Some other model vehicles use four separate speed sensors, with one at each wheel hub location.
Step 2- Clean off dirty connections.
With the sensor removed, find the two contacts where the plug connects. Clean off any dirt or grime that may have built up on both the electrical connector and the speed sensor contacts.
Step 3- Measure the sensor's resistance.
Place one meter lead on each contact while your multimeter is in the Ohms setting. The sensor that is pictured below has a normal resistance of 50 Ohms across the two contacts. Check the service manual for your sensor's specific value.
Step 4- Read the test results.
If the meter reading displays higher than normal resistance, or shows "O.L.", then the internal circuit is electrically open. Similarly, if the reading is lower than it should be, or zero Ohms, then you have a shorted internal circuit. In either situation, the sensor would require replacement.
A few steps to try if the sensor tests good, but you still have an ABS problem.
A dirty sensor probe can cause an incorrect output to the car's computer, and drive an ABS light. If you discover that the sensor is dirty, simply clean it off with some contact cleaner and a rag. After cleaning, reinstall the ABS sensor and see if that fixed your problem.
If the ABS sensor tests good, you may have a break or short in the wires to the sensor. Most likely it will be near the sensor itself because this is usually the dirtiest area in the circuit. If no damage is found near the sensor housing, follow the harness up to the engine or dash connection. Click here to learn how to repair the damaged wire.