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Pelican Technical Article:

ABS Sensor Replacement

Steve Vernon

Time:

2 hours2 hrs

Tab:

$190

Talent:

**

Tools:

10mm wrench, E10 Reverse Torx, flathead screw driver

Applicable Models:

Mercedes-Benz W203 (2001-07)

Parts Required:

ABS wheel speed sensors, 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 on the Mercedes C320 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.

In this article, I will go over how to replace the front and rear ABS wheel speed sensors on your Mercedes W203.

Begin by jacking up and supporting the car, please see our article on jacking up your Mercedes. Remove the front and rear wheels.

With the front wheels off you will see two cables running from the upper fender to the steering knuckle. One will go to the caliper; that is the brake wear sensor. The other cable is the ABS wheel speed sensor and attaches to the steering knuckle. Use a 10mm wrench and remove the bolt holding it to the knuckle. You will need to release the harness from the retaining clips as you go.

The bolt securing the sensor is micro encapsulated, so if you are reusing it, you should clean it up and use a little blue Loctite when reinstalling it.

Use a small flathead screw driver and slip the old sensor from its mount.

Use the same small screw driver and remove the metal clip retaining the connector in the mount on the inner fender well.

Pull the connector from the mount and separate the brake wear sensor from the ABS sensor.

Move to the rear of the car. With the wheel off you can see the speed sensor on the forward part of the hub. Use an E10 reverse Torx and remove the bolt. It too is micro encapsulated and should be cleaned up and reinstalled with a little blue Loctite. Remove the wiring harness from the retaining clips and follow it up to where it joins the connector under the under the rear axles.

Use a small screw driver and release the clip retaining the connector (same as the front) and pull the harness from the connector.

Install new sensors with a thin coating of Molykote Longterm 2 or similar grease to ABS sensor and housing. Install fastener and tighten. Then route wiring harness as it was before and reconnect at housing.

With the front wheels off you will see two cables running from the upper fender to the steering knuckle.
Figure 1

With the front wheels off you will see two cables running from the upper fender to the steering knuckle. One will go to the caliper; that is the brake wear sensor. The other cable is the ABS wheel speed sensor and attaches to the steering knuckle. Use a 10mm wrench (red arrow) and remove the bolt holding it to the knuckle. You will need to release the harness from the retaining clips (yellow arrow) as you go.

The bolt securing the sensor is micro encapsulated (red arrow), so if you are reusing it, you should clean it up and use a little blue Loctite when reinstalling it.
Figure 2

The bolt securing the sensor is micro encapsulated (red arrow), so if you are reusing it, you should clean it up and use a little blue Loctite when reinstalling it.

Use a small flathead screw driver and slip the old sensor (red arrow) from its mount.
Figure 3

Use a small flathead screw driver and slip the old sensor (red arrow) from its mount.

Use the same small screw driver and remove the metal clip (red arrow) retaining the connector in the mount on the inner fender well.
Figure 4

Use the same small screw driver and remove the metal clip (red arrow) retaining the connector in the mount on the inner fender well.

Pull the connector from the mount and separate the brake wear sensor from the ABS sensor (red arrow).
Figure 5

Pull the connector from the mount and separate the brake wear sensor from the ABS sensor (red arrow).

Move to the rear of the car.
Figure 6

Move to the rear of the car. With the wheel off you can see the speed sensor on the forward part of the hub. Use an E10 reverse Torx and remove the bolt (red arrow). It too is micro encapsulated and should be cleaned up and reinstalled with a little blue Loctite. You will need to remove the wire from the retaining clips (yellow arrow) as you go.

Remove the wiring harness from the retaining clips (red arrow) and follow it up to where it joins the connector under the under the rear axles.
Figure 7

Remove the wiring harness from the retaining clips (red arrow) and follow it up to where it joins the connector under the under the rear axles.

Use a small screw driver and release the clip retaining the connector (same as the front) and pull the harness from the connector.
Figure 8

Use a small screw driver and release the clip retaining the connector (same as the front) and pull the harness from the connector. Installation is the reverse of removal

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Comments and Suggestions:
emmanuel Comments: i have ML320 which is in limp mode, i scaned it and got vehicle speed sensor A and vehicle speed sensor circuit open. where is the location for the vehicle speed sensor A?
September 3, 2016
  Followup from the Pelican Staff: Ml320s have the speed sensor inside the transmission. Could be the sensor or a conductor plate issue.- Nick at Pelican Parts  
Sterling Comments: If replacing the brakes can you just re-use the old sensor? Or do you have to get a new one
August 13, 2016
  Followup from the Pelican Staff: If it is not damaged, yes. - Nick at Pelican Parts  
Jamzie Comments: Excellent I'm very pleased has saved me the time and expense.

Thank you keep the good work up.
August 4, 2016
  Followup from the Pelican Staff: Thanks for the feedback. Glad we could help.
- Nick at Pelican Parts
 
lkenney Comments: I am under the impression that there is a ring of sorts that rotates with the wheel that is part of the ABS - I can't find any information on this ring? I believe this ring on my 2001 E320 is broke, therefore sending faulty signal. Any insights would be greatly appreciated.
Thanks
September 5, 2015
  Followup from the Pelican Staff: The tone ring is either on an axle of a wheel bearing. Look into the mounting bore of the sensor to inspect it. - Nick at Pelican Parts  
c240 Comments: TNX PRO
August 31, 2014
  Followup from the Pelican Staff: Thanks for the feedback. Glad we could help.
- Nick at Pelican Parts
 
parklife Comments: Great tutorial. I would have put the car in to the garage if I hadn't seen this. Thanks
July 26, 2014
  Followup from the Pelican Staff: Thanks for the feedback. Glad we could help.
- Nick at Pelican Parts
 
larryb Comments: excellent pictures
May 24, 2014
  Followup from the Pelican Staff: Thanks for the feedback. Glad we could help.
- Nick at Pelican Parts
 
ma32 Comments: i need a video or catalog for a slk320 2001benz how to replace both abs speed sensor do you have
February 25, 2014
  Followup from the Pelican Staff: No we don't. If we get the chance to perform the procedure, we will be sure to document the process. - Nick at Pelican Parts  

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