The ABS wheel speed sensor monitors road wheel movement and sends an electronic signal to the ABS / DSC module. This signal is used to calculate road wheel speed to help with ABS braking and stability control features. Sensors are bolted to each wheel hub and are therefore susceptible to damage from impacts, road grime and brake dust.
BMW X3 models utilize a magneto resistive style wheel speed sensors. This style of sensor allows accurate wheel speed reporting as soon as the wheel moves, unlike the older style inductive sensor that required a speed of about 7 MPH to start working. This allows greater dynamic system control at lower vehicle speeds. This sensor type creates a high to low signal, the low is just above 9 volts, and the high about 12 volts. It is important to use a lab scope when testing these sensors. This being the best way to display the digital signal created by the sensor.
When an ABS wheel speed sensor fails, the ABS / DSC module loses road wheel speed for the corresponding wheel and sets a fault code for ABS wheel speed signal. When a fault code is set, the ABS / DSC warning light will illuminate. You will have to scan the module and read the fault codes to determine which speed sensor is the problem. Keep in mind, other problems can illuminate the ABS / DSC warning light. Be sure to scan and read fault codes before replacing parts.
You can use a scan tool while monitoring wheel speed signals to check for a slower or faster wheel. This can help to pinpoint a faulty sensor. Compare all four wheel speed signals together, look for one that doesn't match the others. To see how to test individual sensor and related fault codes, see our tech article on ABS wheel speed sensor testing.
A faulty wheel speed sensor can set multiple brake warning lights (green arrows). It is important to check for fault codes using a BMW scan tool to identify the problem sensor. It is important to check for fault codes using a BMW scan tool to identify the problem sensor. This helps to identify the problem sensors. To see how to test individual sensor and related fault codes, see our tech article on ABS wheel speed sensor testing.
In this tech article, I will go over how to replace the front and rear wheel speed sensors.
Remember your car may have been serviced before and parts replaced with different size fasteners used in the replacement. The sizes of the nuts and bolts we give may be different from what you have so be prepared with different size sockets and wrenches.
Protect your eyes, hands and body from fluids, dust and debris while working on your vehicle. If working with the electrical system, disconnect the battery before beginning. Always catch fluids in appropriate containers and properly dispose of any fluid waste. Recycle parts, packaging and fluids when possible. Never work on your vehicle if you feel the task is beyond your ability.
Our vehicle may vary slightly from yours as models do change and evolve as they grow older. If something seems different, let us know and share your info to help other users. Questions or want to add to the article? Leave a comment below. When leaving a comment, please leave your vehicle information.
Lift the axle of the vehicle you are replacing the ABS sensor on. See our tech article on lifting your vehicle safely.
Front sensor: The front wheel speed sensor is mounted in the spindle, at the front of the wheel hub. Open the sensor connector housing door (red arrows). Pull the ABS sensor electrical connector out of the holder. Disconnect it by pressing the release tab and pulling it apart. Be careful, these connectors become brittle over time and can crack if squeezed too hard.
Front sensor: Pull the ABS sensor (red arrow) out of the steering knuckle (blue arrow). Then remove it from the vehicle. If the sensor does not slide out easily, pull it out using a pair of pliers. Pull out and wiggle it out slowly. Slide the sensor (red arrow) out of the wheel hub (blue arrow). Install a new sensor with a thin coating of Molykote Longterm 2 or similar grease to the ABS sensor and housing. Install the fastener and tighten. Then route the wiring harness as it was before and reconnect it at the mount.
Rear sensor: To access the rear sensor connector, locate the sensor connector housing splash shield, located just in front of the rear wheel near the trailing arm. Remove the plastic rivet (blue arrows) using a trim panel tool. Then, remove the two 8mm fasteners (red arrows).
Rear sensor: Pull the ABS sensor out of the steering knuckle. Then remove it from the vehicle. If the sensor does not slide out easily, pull it out using a pair of pliers (red arrows). Pull up and wiggle it out slowly. If still stuck, rotate the sensor using a flathead screwdriver. Slide the sensor out of the trailing arm.
Rear sensor: Use a small flathead screwdriver to unclip the wiring harness mounts (red arrow). Then remove the speed sensor wiring from the mounts (blue arrows). Install a new sensor with a thin coating of Molykote Longterm 2 or similar grease to the ABS sensor and housing. Install the fastener and tighten. Then route the wiring harness as it was before and reconnect it at the mount.