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ABS Wheel Speed Sensor Replacement
 
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Pelican Technical Article:

ABS Wheel Speed Sensor Replacement

Tom Morr

Time:

2 hours2 hrs

Tab:

$54-$61 per sensor

Talent:

**

Tools:

Ratchet, T40 Torx bit, 5mm hex/Allen wrench or bit, small flat head screwdriver

Applicable Models:

Mercedes-Benz R170 (1998-04)

Parts Required:

Wheel speed sensors, grease

Hot Tip:

Try cleaning the existing sensors' tips

Performance Gain:

ABS and traction control function properly

Complementary Modification:

Check brake pads and replace if necessary

A faulty wheel-speed sensor reading can trigger the ABS and/or BAS/ASR warning light. A bad wheel-speed sensor signal can be verified with a scan tool that reads the trouble codes.

The actual wheel speed sensor uses a magnetic field to "count" teeth on a reluctor, which spins on the wheel hub or axle shaft. This tooth count is converted into a voltage signal, which the car's PCM uses to gauge wheel-speed variations for its ABS and stability-control systems.

The wheel-speed sensor can go bad, although sometimes disconnecting the sensor and cleaning off accumulated dirt can restore proper function. The car could conceivably be rolled onto ramps for sensor inspection. However, access is optimized by securing the car on jack stands and removing the wheels.

If the sensor needs to be replaced, be sure to clean its retaining bolt(s) and add thread-locking compound to the threads before re-installing these fasteners (Loctite 603 is recommended).

Also, applying a thin coat of grease to the sensor's sides and its mounting hole will help seal out dirt, extending service life. Long-Term Grease works excellently for this project (#000-989-63-51-MBZ from Pelican Parts). The torque spec for the ABS Wheel Speed Sensor Bolts is 8 Nm.

The R170 SLK's front suspension and brakes are somewhat similar to the W203 and many other same-era Mercedes-Benz models.
Figure 1

The R170 SLK's front suspension and brakes are somewhat similar to the W203 and many other same-era Mercedes-Benz models. The brake-wear sensor goes to the caliper; the ABS speed sensor (yellow arrow) mounts in a hole in the knuckle. Use a T40 Torx bit to remove the two bolts (red arrows) that secure the plastic bracket and ABS speed sensor to the knuckle. The ABS sensor wire is held steady by the bracket's rearward clip (purple arrow).

With the bolts removed, the wire unclipped, and the bracket moved aside, the ABS speed sensor (arrow) can be pulled out of the knuckle.
Figure 2

With the bolts removed, the wire unclipped, and the bracket moved aside, the ABS speed sensor (arrow) can be pulled out of the knuckle. A flat blade screwdriver is helpful for prying up on the sensor under the bolt flange.

If the factory retaining bolts (arrow) are being reused, de-grit them with a wire brush.
Figure 3

If the factory retaining bolts (arrow) are being reused, de-grit them with a wire brush. Use blue Loctite for reassembly to prevent the sensor from vibrating loose.

Use a small flat blade screwdriver to gently remove the metal retaining clip that secures the ABS wheel speed sensor and brake wear sensor to the plug in the fender well.
Figure 4

Use a small flat blade screwdriver to gently remove the metal retaining clip that secures the ABS wheel speed sensor and brake wear sensor to the plug in the fender well.

Once unplugged, the ABS speed sensor (arrow) can be separated from the brake sensor and removed from the car.
Figure 5

Once unplugged, the ABS speed sensor (arrow) can be separated from the brake sensor and removed from the car. Reverse the steps to install the new front sensor.

In the rear, use a 5mm hex/Allen wrench or bit to remove the sensor's retaining screw (arrow).
Figure 6

In the rear, use a 5mm hex/Allen wrench or bit to remove the sensor's retaining screw (arrow). The brake backing plate and emergency brake assembly were previously removed here for other articles.

The sensor's wire is secured in a clip (arrow) on the emergency-brake cable bracket.
Figure 7

The sensor's wire is secured in a clip (arrow) on the emergency-brake cable bracket.

Once unbolted, the sensor can be wiggled out of the socket in the knuckle.
Figure 8

Once unbolted, the sensor can be wiggled out of the socket in the knuckle. For reassembly, lightly coat the sensor's sides and knuckle socket with grease.

Cleaning dirt off the sensor's tip and corresponding hub/axle area can sometimes restore proper functionality.
Figure 9

Cleaning dirt off the sensor's tip and corresponding hub/axle area can sometimes restore proper functionality.

Another clip (arrow) secures the sensor's wire to a body-mounted bracket.
Figure 10

Another clip (arrow) secures the sensor's wire to a body-mounted bracket.

The rear ABS wheel speed sensor's plug is in a weatherproof boot under the body tub.
Figure 11

The rear ABS wheel speed sensor's plug is in a weatherproof boot under the body tub. It pulls out of the sheet metal easily.

Set the rear sensor free by unplugging it from the wires that lead to the PCM.
Figure 12

Set the rear sensor free by unplugging it from the wires that lead to the PCM. Reverse the removal steps to install a new rear sensor.

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Comments and Suggestions:
Elmz117 Comments: Hi Nick, My 2001 CLK 230 K has been diagnosed as having a yaw sensor problem, the abs light comes on after a few kilometres, I have tried to look for this part online but not able to find a match. I have tried to find my car model here but I cannot see it. Do you have any suggestions of how much this sensor would cost or where I should look for it? Very much appreciated
November 1, 2016
  Followup from the Pelican Staff: I’m not the best with part numbers.


Give The Pelican Parts parts specialists a call at 1-888-280-7799. They can figure out what part or repair kit you need. - Nick at Pelican Parts
 
ellerjucs1 Comments: my 1998 slk230 stays on first gear, would it be the speed sensor?
September 15, 2016
  Followup from the Pelican Staff: Possible. First check the transmission fluid level to be sure it is correct. Then check the transmission ECM for fault codes. If the system is not working properly, a fault code will be set. This will be your best bet when diagnosing.
- Nick at Pelican Parts
 
martin Comments: Have a 2001 slk230 the abs ,brake,check, pads, bas lights came on for weeks them they go away by them self for some time when the lights are on the top won't work and the speedometer won't work Neither I get code P0500 P0600 and P0243 is a manual 6 speed shift a..any help will b gladly appreciated .. thanks
February 17, 2016
  Followup from the Pelican Staff: This could be a communication issue, data loss between control modules. Do a complete vehicle scan to see if a module is offline, or if other modules have data faults. - Nick at Pelican Parts  
Jon Comments: How can I test each speed sensor using an ohmmeter or multimeter? Do I need to remove each sensor first or can it be done in place? Thanks
January 20, 2016
  Followup from the Pelican Staff: You can use a multimeter or scope to check the signal when the wheel is in motion.
If A/C sensor, it will make about 0.5v when spinning. With scope, a syne wave. - Nick at Pelican Parts
 
SL Comments: Seems like a lot of grease in the sensor cavity. Is this ok?
November 2, 2015
  Followup from the Pelican Staff: I don't see the example of what grease you are referring to. Can you share a photo? - Nick at Pelican Parts  
Loren Comments: I have an SLK230 1999 130K. BAS SAR lights came on n went on a limp mode. Do I replace all abs sensors 2 front n 2 rear?
Let me know. What's your price on oem parts? What else do I need? How long this ship them? In California.
September 1, 2015
  Followup from the Pelican Staff: Could be a sensor issue, but I would start by checking the vehicle for fault codes. If the system is not working properly, a fault code will be set. This will be your best bet when diagnosing.
- Nick at Pelican Parts
 
beemer1100 Comments: BRIIIII LIANT
August 18, 2014
  Followup from the Pelican Staff: Thanks for the feedback. Glad we could help.
- Nick at Pelican Parts
 

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