I recently purchased a 2017 E400 wagon with ~28k miles on it. I've been reading about some common issues and saw many mentions of the cam solenoid and sensors leaking, so I figured I'd check mine. I found oil residue under some of the solenoids and around the base of one of the sensors, but did not find any oil in any of the connectors. I also found oil on top of the valve covers, circled in red, but difficult to see, in my attached picture. I have a few questions regarding these items:

1) Is there any reason I can't just replace the o-rings that seal the solenoids and sensors, rather than replace the solenoids and sensors? What is the advantage of replacing the solenoids and sensors?

2) I saw mentioned that the route of oil into the harness is migration through the plastic bodies of the solenoids and sensors; has this been confirmed? Does this mean that these items are essentially wear items that will migrate oil no matter what? Or is oil seeping past the o-ring and wicking around the plastic bodies?

3) I am having no trouble finding the solenoid harness extensions, but the only sensor harness extensions I have found are some random ones on ebay for the m278. I assume these should be fine, but wanted to know if anyone had a recent verified source of them before risking questionable cables.

4) What source could the oil on top of the valve covers be from? I don't see how any of my solenoid or sensor leaks could get back there, and while I do have a timing cover leak, it does not appear that it could find it's way to that location.


Thanks for whatever input you may have!

Here you go: https://www.fcpeuro.com/products/mer...AaAmVaEALw_wcB

You can buy the kit that includes 2 pig tails or four (if you have four solenoids). You will want to replace the solenoids if they're leaking. You cannot replace the O Rings on the Camshaft position sensors but you can replace the o rings on the camshaft magnet solenoids. However, the issue is that the oil wicks in through the magnets and go through the wire. So replacing the O Ring won't do you any good unless you're leaking oil from the sides of the solenoids.

Valve cover leak: need to reseal it. I just did mine after 160,000 miles. You'll want to fix the solenoids and get the pigtails before it ruins your ECU and wiring harness. That will be a $4,000+ job to fix later on.

Are the replacement sensors and solenoids any different, or will they just continue to have the same oil wicking issue?

Since I don't have any oil in my harness or connectors yet, I'm assuming my oil leaks are strictly from o-rings at the moment. They are a cheap try, so I will be giving it a go.

Why do you say you can't replace the o-rings on the position sensors? I've already removed the o-ring and replacements are a standard size. Is there something else I am missing?

Sounds like all of these oil leaks are more age related than mileage related. This does not bode well for the quality and condition of the seals that are far more difficult to access. Not impressed with the MB quality so far.

They'll leak one way or another. I've replaced one of my solenoids twice in 160,000 miles. The other solenoid was fine and hasn't been replaced yet.

I mean you technically can. But MB doesn't sell the O Rings for the position sensors. Only for the solenoids. You can however go to Harbor Freight or a hardware store and buy o rings for them. Will they be like OEM? prob not. Will they seal okay? probably. Would I risk it? No. I'd get new sensors.

Welcome to the modern day and age of owning a car my friend. They all suck when it comes to QA and materials.

Contact FCP Euro parts support with your VIN and see if they can identify an oring for your camshaft position sensors. I was able to change the orings on Audi engine sensors and avoided replacing the solenoid which was working fine. From what I understand from the TSB, the harness wicking issue occurs when oil begins to pass through the sensor or magnet, not around the external oring seal.

@CaliBenzDriver @S-Prihadi @Sunnyslope48 @W205C43PFL


EDIT*** This reply is on the wrong thread, my bad!

Got it, looks like my plan's coming together. I spoke to FCP Euro on the phone and they recommended this sealant.
One last question

--->Along where exactly is the sealant applied in the engine?

Thank you all so much
- Andrew

If you bought the Permatex for the valve cover leaks, you have to remove the covers, clean them, then apply a bead of sealant on the valve cover flange surfaces before remounting to the heads. The labor time guide is 8.3 hrs for one side and 12.4 hrs to do both sides because there is a lot of component removal required to access the covers.

Use the MB silicon sealant is your best choice here.
Do sand off the cover side magnesium oxide layer to begin with (there is a TSB about doing this).

yes exactly: the CPS leak is internal not the O-ring.

I've had very good results with Permatex on German cars. I believe Elring supplies the MB silicone sealant and you can buy the direct Elring Dirko much cheaper than the dealer option.

Forgot what the part number is precisely, might be this one linked from another thread: https://cimg6.ibsrv.net/gimg/www.mbw...fe21628900.png

these covers need repeat service so sealant better cleanup quickly.
Permatex sure makes great products. I used "blue" to reseal my ISM Module

@alvocado This look like the right one?

- Andrew

Yes, I believe that is the OE equivalent. I always check the product info on the manufacturer website when in doubt. The spec sheets will also include information on set time before final torque, cure time before operating engine, etc.

FYI: here is the original sealant


Mercedes timing cover RTV

Here is the product ID:
MER-003989982010

When using mb (loctite) make sure the product is less than six months old. It has a date on it. It won’t cure if old. I also like reinzosil / reinzoplast products..