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Discussion Starter #1 (Edited)
If you can change a tire then you can change out an ABS sensor, also known as a VSS (vehicle speed sensor) or a WSS (wheel speed sensor). I'm not going to get into how to jack the car as you should already know how to do that SAFELY. I will show you some tools that will make things a little easier. First off I recommend a good torque wrench, you can use a lug wrench but I don't (I like all my lug bolts torqued to specs evenly). You will need a thin wall 17mm socket ($10 for the one in pic w/protective sleeve/Amazon) for the lug bolts if using torque wrench. Also a jack pad tool is in good order as well as a good low profile/long throw jack (2 or 3 ton). Other than that you just need a clip tool or a flat head srew driver and a 10mm wrench. Oh a good light and a bucket to sit on :grin: I don't have my jack stands yet so I'm using blocks for safety, never ever rely on your jack while you work.
 

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Discussion Starter #2
Once you remove the bolts you may have trouble removing the wheel. Striking tire with foot or fist a few times should break it loose, if the wheel hasn't been off in a while it can be worse. The problem is the rotor tends to rust here somewhat bonding the wheel. I'll be sure to clean this up a bit and wipe a thin layer of synthetic lube over the mounting surface as well as the lug bolt threads.
 

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Discussion Starter #3
I'm doing the left front (driver side) which doesn't have the brake wear sensor, just the VSS hence only one harness. The right front (passenger side) has both a VSS and brake wear sensor coming from the wheel hence two harnesses. The VSS connector is located just behind the wheel well cover/liner and can be easily accessed by just removing the two 10 mm fender fasteners and pulling it out of the way (its flexible and will bend). Here is where you get to try your skill at removing the clip, it pulls straight up after you push the side out some. Then just simply remove the plug. The passenger side will have two harnesses connected here to a two harness receiver, one being the VSS and the other the break wear sensor.
 

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Discussion Starter #4
The harness is supported by two clips and carefully routed for no contact with other parts. Be sure to reroute and reconnect the harness properly so it doesn't make contact with the other parts and cause damage to the harness. You can install the new one as you are removing the old one :wink:For the sensor head itself, its a tight spot. Loosen and remove bolt with 10mm wrench and simply slide sensor out. Be sure to keep the foam seal, wipe or wash it up and reuse it.
 

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Discussion Starter #5 (Edited)
My local MB dealer will charge me between $400-500 for this, depends on who you talk to. They will charge me $120 for the part which is $68 on mercedespartscenter.com. By the way the sensors for the front are one and the same part #1729056101 (both right and left) and for all R172 SLK 250, 350 , even 55 AMG. Then they will charge $120 for the diagnosis and $160 an hour for labor and they will use an hour and a half to do it. This took me all of an hour tops, mostly gathering tools and setting up the car. 15-20 minutes on just the sensor itself. These go bad quite often and can be quite a waste of money so don't give someone an easy $500 for doing next to nothing:wink: I also wanted to point out that you would be wise to check all connections first b4 condemning the sensor and replacing it. IMPORTANT-These are active sensors and they can only be tested on the car, you cannot take them off the car and measure resistance across the leads. If you do you will get an Ohm reading of about 8M Ohms and if you reverse the meter leads you will get an infinite reading. You WILL need a good scanner tool with real time or live data feature that can directly monitor and display sensor outputs(basically a mini oscilloscope) to be able to make an accurate diagnosis on a bad sensor.
 

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Mine haven't failed yet (knock on wood), but this seems pretty simple. Thanks for taking the time to document this for us all.
Hopefully they won't, but if they do its too easy. Out of curiosity, how many miles you have on yours now? To have three go bad (right front still not confirmed, could be connection) within 12000 miles or so is concerning to me. Hopefully I just had a run in with a bad batch or something. Ya I plan on doing a write up for every repair that I have to deal with, whether DIY or having to resort to someone on an expert level with the tools to match. I am only intermediate carport level technician:laugh: Hopefully we can get some good repair info on 172's built up in here. On that note I need a favor from you, I'll send you a private message:smile:
 

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Hopefully they won't, but if they do its too easy. Out of curiosity, how many miles you have on yours now? To have three go bad (right front still not confirmed, could be connection) within 12000 miles or so is concerning to me. Hopefully I just had a run in with a bad batch or something. Ya I plan on doing a write up for every repair that I have to deal with, whether DIY or having to resort to someone on an expert level with the tools to match. I am only intermediate carport level technician:laugh: Hopefully we can get some good repair info on 172's built up in here. On that note I need a favor from you, I'll send you a private message:smile:
110K km's about 65K mls en no repair on this item as of yet.
 

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Just had this problem and had it taken care of by a local independent for ~$300. Wish I had seen this first, whoops! I'll definitely be doing this myself in the future. Is the scan tool you've got a MaxiDiag Elite MD802?
 

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Hopefully they won't, but if they do its too easy. Out of curiosity, how many miles you have on yours now? To have three go bad (right front still not confirmed, could be connection) within 12000 miles or so is concerning to me. Hopefully I just had a run in with a bad batch or something. Ya I plan on doing a write up for every repair that I have to deal with, whether DIY or having to resort to someone on an expert level with the tools to match. I am only intermediate carport level technician:laugh: Hopefully we can get some good repair info on 172's built up in here. On that note I need a favor from you, I'll send you a private message:smile:
I got mine replaced under warranty at 3000km.
Then second time replaced in less than 10000km.
I found driving short distance in extreme heat seems to cause my sensors to go bad.

Dealer quoted $1000 USD in my country.
Thanks for the post.
I will try to do it myself later if it come up again.
Is "Maxi Diag Elite" you used a good device for checking this error?
Thanks Sir.
 

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I had an ABS sensor pop last month. My dashboard lit up with all sorts of warnings - ABS,ESP,Tyre pressure warning inoperative etc..... I bought a Carsoft i980 scantool for £99. This was a great buy in case of any future problems. On connecting to the OBD2 port I ran an "auto" scan of all the electronic modules in my 250Cdi. It told me that there was a problem with the RH front ABS sensor. I ordered a new one from Autodoc.fr ( https://www.auto-doc.fr/pieces-detachees/reglage-du-comportement-dynamique-10138/mercedes-benz/slk/slk-r172/13824-250-cdi-d-172-403 ) for about €50 inc delivery & just followed this great guide to fit it. Problem solved & all fault codes cleared using the Carsoft i980.....

The sensors can also be purchased from Piecesauto24.fr

Be aware that the front LH & RH sensors are identical part numbers but the rears each have their own number (ie there are 3 different ABS sensors).
 

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Just had both front Wheel Speed Sensors replaced at the Mercedes Benz Dealer fortunately under warranty so Free of Charge. It was the Right Hand Sensor which was faulty but they have a policy of replacing in pairs. The mileage on my car is 34,000 miles. I am not the original owner so I don't know whether they have been replaced before.
 

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I've never had a sensor fail in 10 years/5 MBs, concerning that they would go on SLKs.

Note that measuring a sensor with a traditional Voltmeter will burn it.
 

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If you can change a tire then you can change out an ABS sensor, also known as a VSS (vehicle speed sensor) or a WSS (wheel speed sensor). I'm not going to get into how to jack the car as you should already know how to do that SAFELY. I will show you some tools that will make things a little easier. First off I recommend a good torque wrench, you can use a lug wrench but I don't (I like all my lug bolts torqued to specs evenly). You will need a thin wall 17mm socket ($10 for the one in pic w/protective sleeve/Amazon) for the lug bolts if using torque wrench. Also a jack pad tool is in good order as well as a good low profile/long throw jack (2 or 3 ton). Other than that you just need a clip tool or a flat head srew driver and a 10mm wrench. Oh a good light and a bucket to sit on :grin: I don't have my jack stands yet so I'm using blocks for safety, never ever rely on your jack while you work.
Looking at google there are many different models of the “Maxidiag Elite”, which model do you have?
 

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I had a front sensor go at 60k miles. Mercedes insisted on replacing both front sensors. Wish I had read this post first! Great post; really useful.
 
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