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Pelican Technical Article:

ABS Brake Sensor Replacement

Kerry Jonsson

Time:

1 hour1 hr

Tab:

$150

Talent:

**

Tools:

E10 Torx socket, 18mm wrench or socket with ratchet

Applicable Models:

Mercedes-Benz W203 (2001-07)

Parts Required:

ABS wheel speed sensor

Hot Tip:

Twist ABS sensor first before attempting to pull out

Performance Gain:

Repair needless ABS activation at low speeds

One of the most important safety developments have been anti-lock brake systems. In the system a sensor mounted in the hub measures the individual wheel speeds of all four wheels. Under braking if one wheel is traveling slower than the others the ABS Computer realizes the wheel is locking up. A locked up wheel no longer reacts to steering inputs and the car will slide until it stops. This reduces the ability of the driver to control the car. Here the ABS Computer can control the brake pressure to the locked up wheel. If the wheel is locked up the ABS computer can reduce brake pressure to that wheel. As the wheel speed sensor indicates the wheel is traveling at the same speed as the others the ABS computer allows pressurized brake fluid to the caliper to continue to slow down the wheels. This process alternates back and forth until the wheel speeds are under control. This allows the driver to come to a safe controlled stop. In this tech article we will go over all the steps to replace the ABS wheel speed sensor.

In order to replace the wheel speed sensor you will need to jack up and support your vehicle see our tech article on jacking up and supporting your vehicle.

The procedure for removing the front wheel speed sensor is the same on the left side as on the right side. In these photographs we are illustrating the right side being removed. Follow the same procedure on the left hand side to change that sensor.

Front Wheel Speed Sensor This Picture illustrates the left side front hub with the wheel removed.
Figure 1

Front Wheel Speed Sensor: This picture illustrates the left side front hub with the wheel removed. We have also removed the brake rotor for photographic purposes but you do not need to remove the brake rotor. Remove the two E10 Torx fasteners (green arrows).

Front Wheel Speed Sensor Remove the heat shield that the fasteners hold down by lifting straight up.
Figure 2

Front Wheel Speed Sensor: Remove the heat shield that the fasteners hold down by lifting straight up.

Front Wheel Speed Sensor Pull the sensor out of the mounting bore in the spindle by pulling it straight up.
Figure 3

Front Wheel Speed Sensor: Pull the sensor out of the mounting bore in the spindle by pulling it straight up. If the sensor is stuck, twist it to free it up.

Front Wheel Speed Sensor Remove the rubber grommets (green arrows) that hold the wiring harness in the brackets.
Figure 4

Front Wheel Speed Sensor: Remove the rubber grommets (green arrows) that hold the wiring harness in the brackets.

Front Wheel Speed Sensor Follow the wiring harness of the wheel speed sensor to its electrical connector.
Figure 5

Front Wheel Speed Sensor: Follow the wiring harness of the wheel speed sensor to its electrical connector. Squeeze the locking tab of the electrical plug (green arrow) and separate the connector by pulling the two halves apart. Installation is the reverse of the removal steps. Plug in the electrical connector and route the wiring harness in the grommet brackets as you found it. Push the sensor straight into the mounting bore in the hub and tighten down the fasteners.

Rear Wheel Speed Sensor ThisPicture illustrates the rear of the rear hub on the right side of the car.
Figure 6

Rear Wheel Speed Sensor: This picture illustrates the rear of the rear hub on the right side of the car. Remove the E10 Torx fastener (green arrow).

Rear Wheel Speed Sensor To remove the sensor pull it straight back out of the hub.
Figure 7

Rear Wheel Speed Sensor: To remove the sensor pull it straight back out of the hub. If the sensor is stuck, twist it to free it up.

Rear Wheel Speed Sensor Twist the wiring harness to remove it from the mounting bracket (red arrow).
Figure 8

Rear Wheel Speed Sensor: Twist the wiring harness to remove it from the mounting bracket (red arrow).

Rear Wheel Speed Sensor Follow the harness to the next mounting bracket and pull the grommet (green arrow) out in the direction of the blue arrow.
Figure 9

Rear Wheel Speed Sensor: Follow the harness to the next mounting bracket and pull the grommet (green arrow) out in the direction of the blue arrow.

Rear Wheel Speed Continue to follow the harness until the sub-frame mount.
Figure 10

Rear Wheel Speed Sensor: Continue to follow the harness until the sub-frame mount. Pull the harness grommet (green arrow) out of the bracket in the direction of the blue arrow.

Rear Wheel Speed Sensor Follow the ABS harness to the electrical connector on the body of the car.
Figure 11

Rear Wheel Speed Sensor: Follow the ABS harness to the electrical connector on the body of the car. Unclip the three plastic clasps (green arrows) that hold the wiring harness in a protective cover.

Rear Wheel Speed Sensor Use a flathead screwdriver to lever out the electrical connector retaining clip.
Figure 12

Rear Wheel Speed Sensor: Use a flathead screwdriver to lever out the electrical connector retaining clip. Now you can pull the electrical connector out of the housing. Installation is the reverse of the removal steps. Plug in the electrical connector and route the wiring harness in the grommet brackets as you found it. Push the sensor straight into the mounting bore in the hub and tighten down the fastener.

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Comments and Suggestions:
Scottyrv Comments: If you still have light on after replacement look at replacingabs sensor bands on driveshafts
March 28, 2016
  Followup from the Pelican Staff: Thanks for the additional info and feedback. We appreciate it.
- Nick at Pelican Parts
 
Jay Comments: What if the sensor breaks in the housing
March 17, 2016
  Followup from the Pelican Staff: Remove it in pieces. Use a small pick to get it out. - Nick at Pelican Parts  
John Comments: To michael skytte, on 8-31-2015 i requested item 1239971681-mbz grommets your reply was there on order. Have you recieved them yet. If so i would like 8 pieces. Thank you jb
September 8, 2015
  Followup from the Pelican Staff: Best bet is to Give our parts specialists a call at 1-888-280-7799. They can help.
- Nick at Pelican Parts
 
DanG2 Comments: Figure 5 for Front Wheel is nor correct, shows same figure as for Figure 6 for Rear Wheel.
January 18, 2015
  Followup from the Pelican Staff: Thanks for catching that. We appreciate it. I will have the article updated. - Nick at Pelican Parts  

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