3

Description of the issue at hand

I just took my car to a mechanic (non-Mercedes specialist) that replaced both front wheel bearings. Other than that, no other repair was made. Other than the bearings making noise, the car was driving fine. Brakes were good.

The repair took a few hours and I got back the vehicle which is driving OK from what I can tell. Only thing is that now there is a warning about tire pressure not being able to be measured, ABS + ESP malfunction and such.

The mechanic said that I should probably take it to a Mercedes dealer for diagnosis (he is not equipped for that). But there is no Mercedes car dealer/garage where I live.

The questions

This is my first Mercedes and have little experience with the brand. Is this a normal behaviour? Should this warning appear systematically after a bearing repair is operated? Should I be concerned even though the car seems to drive fine?

If I manage to "reset" the fault codes associated with the ABS+ESP+Tire Pressure, will that be enough? (I plan on buying a Launch Creader VII+ or an iCarsoft MB II). Or should I really consider taking it to a far away Mercedes dealer and pay ridiculous amounts of money just for a diagnosis?

  • Were those warnings indicating before you took it to the mechanic to replace the wheel bearings? If not, then the mechanic needs to resolve any new issues they have caused during their repairs. They may have forgotten to reconnect a wire harness or something during their work. – CharlieRB Feb 21 '17 at 19:51
  • @CharlieRB No, those warnings were not being indicated at all. They just popped up after I got the car back... – jrojasqu Feb 21 '17 at 19:53
3

The wheel speed sensor is in the proximity of the wheel bearing. Lack of a speed signal from one of these sensors could trigger any of these warnings. Have the mechanic check the sensors, their positioning, and their connections and wiring.

Also, I understand that on this car the encoder ring for the sensor may be built into the bearing or seals and can be damaged or installed incorrectly during a wheel bearing replacement

  • Took the car to the mechanic and insisted that he should check the wiring. The guy re-connected everything. Managed to find someone to do a complete scan by OBDII connector; reset all the fault codes; re-scanned it and it now seems that there are no issues left for now... – jrojasqu Feb 24 '17 at 18:12
2

You don't need to take the car to a dealer. If your mechanic can't do basic troubleshooting than find another mechanic or work on the car yourself. Honestly they should of taken care of the problem to begin with.

Are these press in bearings or are they bolt-in hub and bearing? Is the tone wheel part of the CV shaft or is it a magnetic ring on the bearing? If the tone wheel is on the CV shaft is the tone wheel still there? Is it cracked? Check your invoice, a press in bearing is cheap and it's all labor, bolt-ins tend to be expensive. Ask your mechanic about the tone wheel or pull the wheels off and take a look. You can generally tell which one it is by the location of the sensor.

If it's a press in and the tone wheel (magnetic ring) is part of the bearing the bearing may have been installed backwards.

If it's a bolt in hub and bearing and the wheel speed sensor was reused (or never removed) it's possible that the air gap is off on the sensor due to rust scale.

Another possibility is that the sensor was left unplugged or that the wiring was damaged during the bearing R&R.

If the ABS/Traction light was on immediately after the repair and after starting the car without being driven I'd suspect the wiring is damaged or that the sensor was left unplugged.

As for the tire pressure warning light if your tire pressures are OK see if the system will reset. It's either an active or passive system (possibly a hybrid). If it's an active system, assuming all the sensors work and tire pressures are within 25% of the door label the light should go out. If it's a passive system there should be a button you have to hold down to reset the light. If it is a passive system that would explain why all three lights came on at the same time as the tire pressure monitoring system uses wheel speed data.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.