I'm assuming, but I believe they get oil squirted into them that bypasses the cam adjusters. Many cars, many components, the oil will wick past the sealing silicone or whatever they have in the sensor/solenoid and work it's way into other things, it usually won't cause much of an issue either. But when it does, it's terribly expensive.

 

The cam solenoids are certainly wetted by engine oil but I think capillary action is the prominent explanation for the oil traveling through the wire harness. If you inspect either the solenoid or it's sensor the only barrier or seal at the connectors is epoxy.

Regarding oil appearing to leak from the solenoid onto to the cylinder head ... You'll discover that the three bolt holes are thru holes exposed to the wetted areas. The three bolt hole locations on the solenoids have integrated aluminum crush washers (5mm in height). It would certainly seem that the crush washers should not be reused but you can't remove just the washers. You are supposed to replace the three aluminum bolts. In a financial pinch, I'd reuse the cam solenoid only if there was no suspect oil in the wire harness. I suspect that the oil leaks onto the engine case or cylinder head are caused by torque relaxation because I discovered one of my solenoids showed the beginning of a leak and, sure enough, the lowest bolt had very little torque on it.

 

It must be capillary action. My only other thought would be the oil leaking from the solenoid onto the cylinder head then onto the wiring. Not much the pigtails will do in that case. I ordered the pigtails last night anyway, I certainly have spent $40 in worse ways. Now my question is, what stops the capillary action from going through the pigtails?

I will probably give the mounting bolts a tweak when I install the pigtails. If you have the torque specs handy please share. It is annoying that the seal replaced under warranty 20 months/13k miles ago is leaking. I figured the bolts were one time use as I found one of them on top of the radiator area after the work was done by the dealer. This isn't the first time I have found things left in the engine bay by the dealer service techs and as a result I've decided to do the majority of my own service work from here on out.

 

See attachment.

 

It’s capillary action. Connector orientation doesn’t matter.

-Sensors and solenoids are exposed to oil by design

-sensor body seal fails, because of poor design and manufacture, and allows oil into the sensor side of the connector

-sensor side electrical contacts are wetted with oil

- harness side contacts are wetted with oil by virtue of intimate contact with the sensor side contacts

- oil wicks via capillary action through multi-strand wire harness, in the space between and surrounding the conductor wires.

- oil migrates wherever it can; one endpoint is the engine ECU

 

I agree, mine don't leak yet, but my '03 S500 had a transmission plug that leaked and the oil had worked it's way up the wiring harness almost a foot, against gravity. I cleaned it thoroughly and installed the new plug and gasket, no issue after that.

 

When you get the pigtails, take a peek under the shrink tube. There is some type of component installed between the connector ends. MB or Bosch should have integrated this design fix on the harness from the factory.

 

Check out this video on cap in action:

 

And this for a strategy to mitigate the phenomenon:

https://huesonwire.com/site/wire-and...blocked-cable/

 

Those bolts don't have a sealing washer. They have sealant on the threads because they penetrate into the crankcase and are exposed to oil. They are 1 time use because of the aluminum and because of the sealant. I've had to re-use them because we did not have them in stock (nobody replaces them so they don't get billed out, and don't get ordered for stock), and if you clean them fully and apply good thread sealant on them, they do not leak.

Most of the front cover leaks I saw were the solenoid o-rings sometimes, but usually the covers themselves. They are only sealant, no gasket, and the sealant from production does not stick to the magnesium cover material. When you remove them the first time, all the sealant stays on the head, and none is on the cover. If you remove one that has been previously serviced, you will find the sealant on both surfaces.

 

My car had the oil leak on the front covers repaired under warranty a couple of months ago. I have the pigtails in my closet but was not planning to install until the CPO warranty ends... might just go ahead and do it.

 

Hi everyone. Thanks for your detailed and informative posts. I have learned a lot from them. Recently I was told there was a leak with my camshaft sensor or magnets and decided to check it out myself before paying for the repairs. This is also on a M276 engine. I was able to open the cam sensor harness by pulling up the gray tab and then pinching the gray tab as mentioned in another post, but after few tries I still cant get the cam magnet harness apart. The white tab pulls up and clicks just like the sensor tab but then squeezing or pushing on the white tab does not disconnect the harness and I don't want to break it by pushing it too hard. Any suggestion on how to open this type of harness. Appreciate all your help in advance.


White tab is pulled up and clicks

 

While researching for a solution to the oil in the harness problem, I realized that the fault codes did not correspond to the camshaft sensors at all. They were leaking oil that made a mess around that area of the engine but that's about it. The codes related to random misfire in cylinders 1, 2, and 3. Another code referred to Bank 1 sensor 1, and bank 1 sensor 2 - those were the two pre and post-cat O2 sensors.

So I went ahead and bought 4 camshaft sensors (also called camshaft adjuster electromagnets) for $204 for 4, to take care of the oil leaks and the two O2 sensors @230 for both. Took me about two hours to replace 3 of them that were leaking. The fourth one was not leaking and I also could not access its bolts as they were behind the huge air intake on the M276 engine, so I left it as it was. I then took the car to a local mechanic that I know and asked him to replace the two O2 sensors. The car is working perfectly since that day. No more oil leakage. No more misfiring.

 

@Aftab Thanks for the post. Please update us in 1-3 months. Did you replace the wiring harness?

Electromagnets are not the cam sensors.

4 electromagnets control position of the cam adjusters and the camshafts

4 cam position sensors measure the actual position of the camshafts

Therefore 8 pieces of hardware that are exposed to oil and can potentially leak oil into the harness.

@LILBENZ230 What is the part number for the pigtails you are in possession of? I wonder if they would fit on other vehicles using the M276. What do you think?

 

You are right. I only replaced the electromagnets and O2 sensors. I did not install pigtails.

 

Scroll back in this thread and there should be part numbers and photos of my installation.

 

271-150-0156 is the part number

 

That video doesn't really demonstrate capillary action so much as pressure differentials pushing water (or, more to the point of this thread, oil) around thanks to thermal differences causing expansion and contraction.
Capillary action gets water up to tree leaves way up off the ground. Or oil from a connector to the other end. No pressure involved.

 

Indeed, you're correct.
Surprised it took that long for a contributor to mention that. I thought about that, unfortunately, a few days after I posted it. Ironically, I tell my kids to always double check when you're researching stuff on the net; clearly, I didn't practice what I preach.

Anyway, the take away from the video is that the delta P (caused by the temp differentials) is causing to the blue water to migrate.

 

Has anybody had these isolator harnesses installed for a long period of time/miles with no incidence of oil penetration? How do these isolator harnesses prevent this issue, because can't the oil work it's way across the isolator harness to the engine harness like it does normally? I'm assuming you'll still have to regularly check the solenoid for seepage and replace at first signs of oil.

My mother had this issue with her 2012 ML350, and it was a costly repair like others have stated. I'm in the market for a used C350, but this issue singlehandedly excludes 2012-2014 facelifted cars from my search.

 

I had the pigtails installed on my W203 and it stopped all leaks - car had 150,000 miles when I got rid of it and had never had the issue.

The M272 had its own issues, so you're doing yourself a disservice by not including the 2012-2014 C350s in your search. We had a 2014 C350 a few years back.. great car.

 

I thought I read (here?), that the updated parts didn't make it into production until MY '16 cars - someone please correct me if I have this wrong... And I too would not exclude the years before - just watch for it and/or be proactive on the pigtails, or choose a less expensive fix than what MB does: shops and individuals have successfully cleaned an oiled harness...

 

Good question Richard. If MB believes the isolator harness is a solution, it tells me that the factory connector on the harness end is not leak proof, and that the isolator harness connector is leak proof. The question remains, what are the design aspects of the isolator harness that makes it leak proof.

Many vehicles (Volvo trucks, BMW, others) have had this problem. Seems like the time span is 2010 +/- a couple of years.

Here is a Toyota Supra thread with similar/same symptoms from the mid-2000s. There is probably a design similarity or shared vendor between Toyota and Mercedes for these sensors. Could be Bosch or Denso.

https://www.supraforums.com/threads/...d-wire.509818/

 

Thanks, Chassis! Great info.

So your W203 was leaking before installing the isolator harnesses, and afterwards, not another issue? That sounds promising! And I certainly don't want to exclude 2012-2014 C350's from my search. I had a 2009 C300 for 10 years, and it was amazing aside from the EIS/ESL issue. Maybe I'm overreacting about the oil-in-harness issue. I'd jump at a nice C350 coupe right now. lol

Is the updated part that you're referring to the updated part number for the cam solenoid mentioned earlier in this thread, or is there a totally new part from a newer car that can be retrofitted? I read about this issue a couple years ago when it happened to my mother, and I just came across this thread shortly after starting to look for another W204. I'm definitely reconsidering the facelift C350 now after reading this thread. There's a great MB indie by me, too.

 

Correct. Car was a 2005 C230K and at 55,000 miles it had just started to leak. Installed the pigtails as they were called and never had any issues.