The BMW E39 has an electronic wheel speed sensor located at each hub. In the simplest terms, the car uses these sensors to count the number of rotations made by each wheel. It monitors each one to recognize if one or multiple of the wheels are slipping or are locked up. This is how the car’s stability control and anti-lock brake (ABS) systems regulate themselves. If one of the speed sensors is malfunctioning, the car gets an erroneous count from that particular wheel.
Replacement of the E39 wheel speed sensors should only take about 15 minutes per wheel and can be done in your garage or in your driveway with relative ease.
BMW models and years applicable:
Symptoms & diagnosis of a failing BMW E39 wheel speed sensor:
- non-functioning ABS
- non-functioning traction control
- non-functioning speedometer
- non-functioning odometer
- non-functioning cruise control
One of the most glaring signs that one or more of the wheel speed sensors or ABS sensors on your BMW E39 has either died or on its way out is when you see three warning lights on your dashboard. These warning lights will be the ABS light, BRAKE light, and finally the TRACTION LOST triangular warning light. If you have these lights, your next steps will be trial and error to figure out which sensor is at fault. Driving without traction control or ABS is dangerous and should be avoided whenever possible.
The discussion of wheel speed sensors and their diagnosis has filled many forum pages over the years. The three best ways to diagnose which sensor is going bad are:
- Use an advanced diagnostic tool that can read BMW’s proprietary codes (A simple OBDII scanner will not suffice.)
- Visual inspection. In my case, many of the wires showed evidence of wear. This is not uncommon since the sensor wires are constantly exposed to road debris.
- Use a multimeter to test for an "open" condition or "OL"
Tools needed to replace a BMW E39 wheel speed sensor:
- Floor Jack
- Jack Stands
- Wheel chocks
- 5mm hex socket
- Small flat-blade screwdriver
- Plastic trim removal tool
- 8mm wrench
Parts needed to replace a BMW E39 wheel speed sensor:
- Front Wheel Speed Sensor – 34526756375
- Rear Wheel Speed Sensor (sedan) – 34526756376
- Rear Wheel Speed Sensor (wagon) – 34526756377
How to replace a front wheel speed sensor
Start by putting the transmission in park, and setting the handbrake. Raise the car and safely secure it on a jack stand for the side that you plan to repair.
There should be a black box on your inner fender that contains the wheel sensor plug. Open the box carefully with a flat blade screwdriver here.
Depending on which side of the car you're working on, there may be one or two sets of wires inside this box. The light blue one will typically be for the wheel sensor (ignore the wire that runs to the brake caliper; this is a brake wear sensor).
Remove the connectors from the box. Press on the tabs and separate the two connectors.
Use a 5mm Allen wrench to remove the two bolts that connects the wheel sensor to the hub assembly.
Pull out the old wheel speed sensor.
Install the new sensor and tighten the bolts.
There are two points to secure the wire from rubbing against the tire.
Reassemble the connectors.
Install the connectors in the black box.
Reinstall the wheel, lower the car, and go for a test drive.
How to replace a rear wheel speed sensor
Chock the front tires, and raise the car on the side that you want to repair. Remove the wheel.
Depending on which side of the car you're working on, you may see one or two wires leading to the wheel. Ignore the wire that runs to the brake caliper. This is the brake wear sensor. The wheel speed sensor is attached to the top of the wheel hub. Its connector is hidden behind the rearward fender liner.
Loosen the plastic fender liner by undoing the retainer clips and removing the plastic 8 mm bolts.
Loosen the rearward portion of the fender liner. Be careful not to tear it. Remove the blue connectors from their case behind the fender liner.
Separate the connectors by squeezing the tabs and pulling the plugs apart.
Use a 5mm Allen wrench to remove the bolt securing the wheel speed sensor to the hub.
Pull the sensor out of the wheel hub. Take note of how the old wire was routed through it mounting points.
Connect the new speed sensor to the wiring harness. Install the connectors in their mounting box.
Feed the wire behind the fender liner. Pass it through all its mounting points.
Install the sensor in the hub and tighten and its bolt. Then reinstall the fender liner and its retainers and bolts.
Make sure that the sensor wire will not rub against the tire. If there is too much slack in the sensor wire, feed some of it back behind the fender liner.
Reinstall the wheel, lower the car, and take it for a test drive. It may take one or two drives for the dashboard warning lights to turn off.
And that's it, you should have brand new, functioning wheel speed sensors on your BMW E39. If you are still running into problems, or have any other questions about this process, leave them in the comments section below.
Alex is FCP’s Blog Editor and a Desktop Engineer from Endwell, NY. He has over 9 years of experience working on a wide array of import makes, but has found his home with European cars. With a BMW and Volvo at home, the garage is always busy.