Testing and Replacing Wheel Speed Sensors

[Jimmyboy]

SLK 200K WDB170 miles 90,000 miles 2001

Hello, I have been reading a recent post by 'Knowlap' regarding ABS and ESP faults. 'Television' advises that my problem is a wheel speed sensor. I have looked behind a front wheel but am not sure how to get the sensor off. It appears to be behind a plate and cover held on with two quite substantial torque screws. Also the cable goes up and through the wheel arch where it joins up with the brake wear sensor cable - cannot trace any farther. Could someone please advise:

a) Can I safely take off the plate/cover and pull the sensor out?
b) Does the cable disconnect from the sensor so I can check the resistance?
c) What approximate resistance value am I looking for (a few ohms or kohms)?
d) Are the rear sensors a similar arrangement?
e) I assume the sensors are just two wire??
f) Any other tips MOST appreciated.

Many thanks for help.

Jimmyboy

 

[Alex Crow]

SLK 200K WDB170 miles 90,000 miles 2001

Hello, I have been reading a recent post by 'Knowlap' regarding ABS and ESP faults. 'Television' advises that my problem is a wheel speed sensor. I have looked behind a front wheel but am not sure how to get the sensor off. It appears to be behind a plate and cover held on with two quite substantial torque screws. Also the cable goes up and through the wheel arch where it joins up with the brake wear sensor cable - cannot trace any farther. Could someone please advise:

a) Can I safely take off the plate/cover and pull the sensor out?
b) Does the cable disconnect from the sensor so I can check the resistance?
c) What approximate resistance value am I looking for (a few ohms or kohms)?
d) Are the rear sensors a similar arrangement?
e) I assume the sensors are just two wire??
f) Any other tips MOST appreciated.

Many thanks for help.

Jimmyboy

I would say that removing the sensors for inspection/testing is probably going to be a waste of time, and you may well break them.
But my answers are...

a) Yes, but be careful not to damage it if it is tight.
b) Connection point is in the wheel arch (shared with brake wear wiring) , and the best place to test a sensor, but...
c) Some of these sensors read almost open circuit anyway, so a resistance check will not help much. I would suggest if you are determined, to measure the AC mV at the sensor when spinning the wheel, and compare values.
d) Rear sensors are similar or same in function, but very prone to seize in position, and easy to damage if removing.
e) Sensors are 2x wire.
f) Yes, start with the fault codes!!!!!!!!!!!!!!!!
If it is just a brake pedal switch, you will be doing a lot of work for nothing.

Now, can I ask, what problems are you having with it?

 

[Jimmyboy]

Thank you Alex. I will take your advise and test the mV from the plug which I assume from what you say can be disconnected at the wheel arch. My problem is that the ABS warning light and the ESP/BAS warning light stay on permanently (for the last few days). I have tested the codes and my simple reader comes up with P0500 (Wheel Sensor A malfunction) I have cleared this code using the reader (and also disconnected/reconnected the battery) but the lamps come on immediately the engine is started, without moving the car (so without rotating the wheels!!). That's it. Needless to say the cruise control doesn't work but no other apparent problem.

 

[Alex Crow]

OK, so you have a fault code in the engine management, pointing to 'CAN message from ESP - speed signal implausible.

This does not directly point to an individual speed sensor/signal fault in the ESP system. I can only suggest you need to go into the actual module in question here (ESP module) and do fault code analysis from there.

Many good specialists will read out the codes, do few checks and advise for an hourly charge only. For half an hours work in our workshop you will be looking at a £30 bill, including the VAT - hopefully that will give you an idea of what to pay.
I would only consider using a reputable Mercedes specialist for this work, if I were you.

 

[Jimmyboy]

Hello Alex, Unfortunately you are a bit far away, I live in E. Sussex. The nearest independent I know and have used is in Southampton. The main MB dealer near here tends to recommend replacing parts that are not really necessary, so I am not too happy with them. Anyway, I will take your advice and compare sensor outputs first without attempting to remove them.

 

[Alex Crow]

Hello Alex, Unfortunately you are a bit far away, I live in E. Sussex. The nearest independent I know and have used is in Southampton. The main MB dealer near here tends to recommend replacing parts that are not really necessary, so I am not too happy with them. Anyway, I will take your advice and compare sensor outputs first without attempting to remove them.

I was not suggesting you bring it here!
Just giving an idea of what I see as the best way forward...