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Audi A4 ABS Wheel Speed Sensor Replacement
 
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Pelican Technical Article:

Audi A4 ABS Wheel Speed Sensor Replacement

Steve Vernon

Time:

1-4 hours

Tab:

$110 to $580

Talent:

**

Tools:

5mm Allen, floor jack, jack stands, wheel chocks, torque wrench, auto creeper, safety glasses

Applicable Models:

Audi A4 (2002-05)
Audi A4 Cabriolet (2003-06)

Parts Required:

ABS wheel speed sensors, high temp grease

Hot Tip:

Check for fault codes before replacing

Performance Gain:

Working ABS brakes

Complementary Modification:

New brake pads

The ABS wheel speed sensor on the Audi A4 monitors road wheel movement and sends an electronic signal to the ABS module. This signal is used to calculate road wheel speed to help with ABS braking and stability control features. When an ABS wheel speed sensor fails, the ABS 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 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 warning light. Be sure to scan and read fault codes before you start replacing expensive parts.

The sensor is basically a magnet that picks up a signal from a ring in the wheel hub. The ring has equal areas of metal and open space that the sensor uses to determine how fast each hub is spinning. This information is used to calculate if one wheel is turning at a different speed than the other and this information, in conjunction with information from other sensors is used by the ABS system to modulate the brakes and prevent one wheel from locking up.

The sensor sits very close to this ring so it is important when replacing the senor that it is sitting flat and flush in its mount and does not come in contact with the ring.

While you may be able to perform this work while lying under the car with the wheels on, I recommend doing this job with the car safely in the air. Begin by jacking up and supporting the car. Please see our article on jacking up your Audi. Remove the front and rear wheels.

Front Sensor- The front wheel speed sensor is mounted on the wheel bearing housing (red arrow).
Figure 1

Front Sensor- The front wheel speed sensor is mounted on the wheel bearing housing (red arrow). The cable for the sensor is connected several places, including the wheel bearing support (yellow arrow) as it runs up the wheel well.

Front Sensor- Use a 5mm Allen and remove the single bolt holding the sensor in place.
Figure 2

Front Sensor- Use a 5mm Allen and remove the single bolt holding the sensor in place. Pull the sensor straight back and out (red arrow). When installing make sure to clean the mount area so that the sensor can mount straight and flush and does not come in contact with the wheel hub ring.

Front Sensor- Disconnect the cable from the retaining clips.
Figure 3

Front Sensor- Disconnect the cable from the retaining clips. The cable houses the wiring for the brake wear sensor (yellow arrow). Disconnect the connection and remove the cable from the retainer (red arrow).

Front Sensor- Unclip the cable from where it mounts in the bracket by the brake line (red arrow).
Figure 4

Front Sensor- Unclip the cable from where it mounts in the bracket by the brake line (red arrow).

Front Sensor- Follow the cable until it enters the chassis.
Figure 5

Front Sensor- Follow the cable until it enters the chassis. If needed, use a screwdriver and gently pry the grommet out from the wheel well (red arrow).

Front Sensor- Pull the cable out from the opening and unplug the cable.
Figure 6

Front Sensor- Pull the cable out from the opening and unplug the cable. Installation is the reverse of removal. Note: use a little dish soap to help get the grommet back in place.

Rear Sensor- The rear ABS sensor is mounted on the top of the wheel bearing support (red arrow).
Figure 7

Rear Sensor- The rear ABS sensor is mounted on the top of the wheel bearing support (red arrow).

Rear Sensor- Use a 5mm Allen and remove the single bolt holding the sensor in place.
Figure 8

Rear Sensor- Use a 5mm Allen and remove the single bolt holding the sensor in place. Pull the sensor straight back and out (red arrow). When installing, make sure to clean the mount area so that the sensor can mount straight and flush and does not come in contact with the wheel hub ring.

Rear Sensor- Follow the cable back to where it enters the chassis.
Figure 9

Rear Sensor- Follow the cable back to where it enters the chassis. It is clipped to the vehicle in several places including the lower arm (red arrow). Use care when unclipping the cable, as the clips become brittle with age.

Rear Sensor- The connection for the rear ABS cable in in the rear section of the passenger compartment on each side.
Figure 10

Rear Sensor- The connection for the rear ABS cable in in the rear section of the passenger compartment on each side. Remove the lower seat cushion and gently pry the side bolster away from the vehicle. This will give you enough room to change out the connections. Installation is the reverse of removal.







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Comments and Suggestions:
Henderson100 Comments: Could anyone please tell me the length and thickness of the bolt that holds the rear sensor in? I need to drill it out and would like to have one to hand to replace it thanks
May 31, 2016
  Followup from the Pelican Staff: I don't have that info. The Pelican parts specialists can get you the fastener. Give The Pelican Parts parts specialists a call at 1-888-280-7799.
- Nick at Pelican Parts
 

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