Cheap R172 Front Speed Sensors

[2012SLK200]

It seems the speed sensors on the front of the R172 SLK are a weak point. They quit and a plethora of lights turn the dash into a Christmas tree, and the OBS-II throws off a ton of errors. The way to verify is to put your OBD reader into dynamic mode, take a slow drive and have your passenger watch the speed of the 4 wheels. The one showing 0.6 km/h is the bad one.

Next comes the fun part... shopping. Unless of course you like taking it to the dealer and paying three or four figures, but get the free coffee and loaner car.

Part number 1725400017 fits left and right front.

• The local aftermarket shop had an ATE brand for NZ$166 ($US104) plus $7 shipping. And that's their discount price. RRP is NZ$195.81 ($US121/£100)
  • To be fair, this price includes our 15% sales tax so the real price before tax is US$90.
• Pelican had a genuine MB for US$102.25 plus $81.75 shipping to NZ. not sure if they collect NZ 15% tax or not
• FCP Euro also had the genuine part for $100.49 plus $36.83 shipping. Ditto on the tax
• Rock Auto had several choices, and I chose their Holstein 2ABS3206 that was US$20.00 plus $14.50 shipping plus 15% tax. So I ordered two, and the shipping remained the same.

The order was on 14 August 2022, and it arrived USA to my island in NZ on 25 August
I installed it, cleared the codes, it showed speed on the Live Data, and on the test drive no more errors.
It works. I'm happy.

I also found the same part on AliExpress. "https://www.aliexpress.com/item/1005004232739497.html".

• I paid US$3.85, $2.48 shipping. Total amount US$6.33. So, for a lark, I ordered it too.
• They estimated delivery on 14 Sept 22, but 25 August, it appears to have cleared Auckland Airport and should arrive in a day or two.
• $3.85 - that's crazy. Or maybe there are just too many intermediaries between the factory that churns these things out and the retailers we use.

When the Rock Auto package arrived, it said "Made in China", leading me to suspect the same factory that made the Holstein part makes the no-name AliExpress.

The no-name sensor from China arrived today, a day after the Rock Auto Holstein sensor arrived from the USA. I ordered it a day after Rock Auto, so it seems global shipping is back to normal. They said to expect it in mid September, so ordering on 15 Aug, and getting it on 26 August is not bad... and that included the extra day it takes to send it over on the ferry from the mainland.

This is the package.

This is the invoice

This compares all three

They look like they all were made in the same factory. The MB and the No Brand have the same colour orange. The Holstein is closer to red. The Mercedes has its tri-star in the plastic, the others do not, although the Mercedes and the No Brand have a circular date stamp. All three are identical in size, with the mounting points in exactly the same place. The cables between the Holstein and the No Brand look exactly the same except no white text on the No Brand.

I have no idea what the mark up from the factory to the "Drop shipping car Parts Store" is, but it certainly tells a story. From the appearance, the $3.85 sensor looks exactly the same as the far more expensive MB Original, and while I have not tested it, I would expect it will work. After all a sensor is not a particularly sophisticated device. I have one on my ebike and all it does is send a pulse every time the magnet on the spoke passes by.

Forums tend to have members with very different views, often strongly held. Some will never buy anything but the official MB part, and disparage anyone who buys less. In some cases they are right, the aftermarket is of poorer quality. But MB actually makes very little anymore. It employs buyers who purchase from factories, and most of the German factories have closed. Some parts are made in eastern Europe, but quite a few in China. Looks like I found the MB source. The factory did its expensive run for MB that added markup after markup. It then did a run for the secondary market but removed the logo stamp. It then kept the same machine going to make a run using up the rest of the raw materials, which it sticks on AliExpress.

I'm tempted to stock up on a few of these, front and rear. For the price of a burger, why not?

As of February 2023, there are 2989 left.

 

[leef44]

Well that is quite a find, thank you for that! They seem to have quite a catalogue. That mark up is crazy!

I had mine replaced at a Specialist since I'm a numpty with these things. Are they quite easy to replace yourself?

 

[2012SLK200]

Well that is quite a find, thank you for that! They seem to have quite a catalogue. That mark up is crazy!

I had mine replaced at a Specialist since I'm a numpty with these things. Are they quite easy to replace yourself?

Yes, they are easy to replace, just unbolt, pop off a spring, unclip and install the new one in reverse order. Except that "just" is in the ideal world, once you have done one, and your car looks like factory new. In realty, things don't want to come out easy, and it's hard to see what you are doing.

So here is a complete step-by-step that I posted on another forum back in August. I make a practice of paying forward, as do others upon whose shoulders I stand.

2012 R172 RHD JDM

The failure of one left front sensor lit up the dash and the OBD-II reader displayed the following

2 faults on the ECM

• C003100 - The left front wheel sensor is faulty and
• C003164 The left front wheel sensor is faulty. An implausible signal exists

1 fault on the VGS (transmission control),

• U1409 The left front wheel speed signal from the traction system is unavailable on the CAN bus

An exclamation mark on the ESP

• C110200 The signal of the component 'L6/1 (Left front axle RPM sensor) is implausible
• C327100 Implausible values of RPM sensors on front axle
• C326600 Consequential fault

1 fault on the PTS (Parking system)

• C41500 Data received from the ESP control module were implausible

1 fault on EFB (Electric Parking Brake)

• U01200 Communication with the ESP is faulty

I left the Autel MP808 reader on, in dynamic mode and took a test drive. Sure enough three wheels read 20 km/h and one 0.6 - the left front. It was dead.

Part number 1725400017 fits left and right front.

Installation.

There are numerous threads documenting how to replace the sensor, but they all seem to spend a lot of time telling you how to safely jack up the car, but are vague on the stuff you really need to know. The most annoying are the videos where the guy's hands block the camera so you can't see which way the retaining spring goes.

So here is the shade tree version...

I did the left side only. Access is easier if you turn the wheel hard left.

The wheel side of the sensor is held by a 10mm bolt but in my car, access is really tight. The first time I used a slim ratchet wrench. Big mistake because it is so tight that when the bolt gets out to a certain point, you can't remove the wrench and the type I used can't be reversed. I had to grip the threads with surgical clamps to give me enough clearance to get the ratchet wrench off.

Use an old fashioned open end wrench. It is a slow job. Here is the closeup:

Aligning the bolt on installation of the new sensor is not easy. I found I had to use some surgical clamps to hold the threads until it caught. Then I could barely get my finger into hand-turn and finally could use the wrench.

To access the other end you have to remove two 10mm plastic nuts holding the plastic wheel well. They are obvious which ones. Of course you can pull the whole thing off, but that is in the too hard basket for a shade tree mechanic. I found I could grab and move the flexible plastic with a pair of vice grips and hold it out of the way. But it is tight.

Once you expose the upper sensor plug, you will find it is held on with a silver clip. I'm lucky, my car has zero rust and looks like its previous Japanese owner (before import to NZ) never drove in rain, much less snow or crud. Your clip might be rust coloured. I don't know what it is made of.

This photo makes it look easy. It is not. It's easy to get a camera in. Hard to access with normal-man-size hands. You take a screwdriver and try to pop the silver spring upward. It is hard to access, hard to see, you need a really long, large flat-head screwdriver and it resists being removed until it finally pops off, goes flying and hides in the plastic cover underneath the wheel mounts... or just about anywhere. A smart shade tree mechanic just orders a replacement before they start the job. But even though I had read about this in one forum post, sure enough mine went flying off and of course landed in an inaccessible place. But by banging on the lower plastic, I heard it, and was able to spot and retrieve it. The other alternative is to tape cloth all around so it flies off, hits the cloth and falls where you can find it.

This is the spring

This is what the housing looks like after you replace the sensor but before the spring.

Then with both ends hooked up, ensure the sensor cable is snapped into the two middle cable holders that keep it out of harms way:

The upper clip is hard to see

And that is it. Bolt the plastic wheel wheel back into place, put the wheel on, clear the codes and take for a test drive.

The sensor I removed looks like a MB branded. The MB branded sensor looks absolutely identical to the Holstein part, except the Holstein has its name on the cable.

Update 6 months later - works fine, no issues. No error codes on the OBD-II reader