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ABS Wheel Speed Sensor Replacement
 
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Pelican Technical Article:

ABS Wheel Speed Sensor Replacement

Nick Czerula

Time:

2 hours2 hrs

Tab:

$150

Talent:

****

Tools:

Pliers, 5mm Allen bit, 8mm socket

Applicable Models:

BMW Z4 Convertible (2003-06)
BMW Z4 Coupe (2006)

Parts Required:

ABS wheel speed sensor, Molykote Longterm 2 grease

Hot Tip:

Check for fault codes before replacing

Performance Gain:

Repair faulty ABS sensor

Complementary Modification:

Properly route wiring, use new clips if needed

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 Z4 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 older style inductive sensors 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 is 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 also set multiple brake warning lights (green arrows). It is important to check for fault codes using a BMW scan tool. This also helps to identify the problem sensor. 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 (red arrow), between the strut (blue arrow) and the wheel hub.
Figure 1

Front sensor: The front wheel speed sensor is mounted in the spindle (red arrow), between the strut (blue arrow) and the wheel hub.

Front sensor: Open the sensor connector housing door (blue arrow).
Figure 2

Front sensor: Open the sensor connector housing door (blue arrow). Pull the ABS sensor electrical connector out of the holder. Disconnect it by pressing the release tab (red arrow) and pulling it apart. Be careful, these connectors become brittle over time and can crack if squeezed too hard. 

Front sensor: Remove the sensor wiring harness from the mounts (red arrow) on the body and strut strut by pulling them straight out.
Figure 3

Front sensor: Remove the sensor wiring harness from the mounts (red arrow) on the body and strut strut by pulling them straight out.

Front sensor: Working at the steering knuckle, remove the ABS sensor 5mm Allen fastener (red arrow).
Figure 4

Front sensor: Working at the steering knuckle, remove the ABS sensor 5mm Allen fastener (red arrow).

Front sensor: Pull the ABS sensor out of the steering knuckle.
Figure 5

Front 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. Pull up and wiggle it out slowly. If still stuck, rotate the sensor using a flathead screwdriver (red arrow), the sensor will be removed with the fastener (blue arrow) still in the sensor housing.

Front sensor: Slide the sensor (red arrow) out of the wheel hub (blue arrow).
Figure 6

Front sensor: 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: The rear sensor in mounted in the rear swing arm behind the brake rotor backing plate (red arrow).
Figure 7

Rear sensor: The rear sensor in mounted in the rear swing arm behind the brake rotor backing plate (red arrow).

Rear sensor: The connector is located behind the wheel well liner (red arrow).
Figure 8

Rear sensor: The connector is located behind the wheel well liner (red arrow). Blue arrow points to the trailing arm for orientation.

Rear sensor: Remove the 8mm fastener (purple arrow).
Figure 9

Rear sensor: Remove the 8mm fastener (purple arrow). Remove the 10mm plastic nut (red arrow). Then remove the two plastic rivets (blue arrows). Pull the section of wheel well liner down and off the fender.

Rear sensor: Open the sensor connector housing door (red arrow).
Figure 10

Rear sensor: Open the sensor connector housing door (red arrow). Pull the ABS sensor electrical connector out of the holder. Disconnect it by pressing the release tab (blue arrow) and pulling it apart. Be careful, these connectors become brittle over time and can crack if squeezed too hard. 

Rear sensor: Remove the sensor wiring harness (blue arrow) from the mounts (red arrows) on the trailing arm.
Figure 11

Rear sensor: Remove the sensor wiring harness (blue arrow) from the mounts (red arrows) on the trailing arm. Hold the mount open with a small flathead screwdriver as you remove the harness.

Rear sensor: Remove the sensor wiring harness (blue arrow) from the mounts on the trailing arm by pulling it straight out.
Figure 12

Rear sensor: Remove the sensor wiring harness (blue arrow) from the mounts on the trailing arm by pulling it straight out. Then feed the wiring harness (red arrows) through the hole in the trailing arm.

Rear sensor: Working at the trailing arm, remove the ABS sensor 5mm Allen fastener (red arrow).
Figure 13

Rear sensor: Working at the trailing arm, remove the ABS sensor 5mm Allen fastener (red arrow).

Rear sensor: Pull the ABS sensor out of the steering knuckle.
Figure 14

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. Pull up and wiggle it out slowly. If still stuck, rotate the sensor using a flathead screwdriver (red arrow).

Rear sensor: Slide the sensor out of the trailing arm.
Figure 15

Rear sensor: Slide the sensor out of the trailing arm. 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.

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Page last updated: Mon 3/27/2017 03:05:27 AM