On our 550 when oil got into the wiring harness, the only fix approved by MB was pull the engine and replace the entire wiring harness and 4 cam position sensors with updated parts - they also inspected every connection point the harness goes to and if oil was found, they replace the component the harness attaches to (ours had zero). I asked about having to worry about this happening again and was told these were updated parts and it wouldn't happen again. From what I read (somewhere) the new parts went into vehicles starting MY 2016...

BIL has an '12 E63 (they can have the same issue) - he asked his indy shop about doing the pigtails proactively and they said they inspect for oil infiltration on every vehicle that's prone to it, every time they lay hands on one - they've had 100% success just cleaning the oil out of the harness and replacing faulty parts. So the MB fix is extremely expensive...

You might just pop into your indy shop and ask about what they do - that should give you confidence in looking at this range of models...

This is great information. A second opinion is always smart. MB seems to want to replace the whole harness and ECU immediately without even attempting cleaning, but that's the dealer for you.

My CPO warranty is going to expire soon - what should I be looking for with this 'oil leak under the front covers'?

@mtnman82 The M276 3.5L NA engine can leak in these areas:

rear main seal (not the topic of this thread), can be viewed from beneath the vehicle if leaking
cylinder head front covers
cam magnets/solenoids
cam position sensors
cam covers

Thank you!

I finally got around to installing the pig tails today while I was doing other service work. The ends of the factory connectors looked to be oil free but I installed them anyway. They are a little tricky, but I found the easiest thing was to pop the white tab up then squeeze it with needle nose pliers and wiggle the connector off. I did have to unbolt the air filter box to gain access to the one on the furthest passenger side. It appears that if you install the pigtail with the white clip in the same orientation as the original, then align the “square” sides on the other end you will get the wires oriented correctly.

@up_too_late Great work. Can you please post photos, parts numbers, and your VIN to help other readers? Thanks.

If I have oil in the ECU, do I have to get a new ECU or is it fixable? I’m still tried to find out how the oil got in there. I have an M276 engine. 2012 E350. Thanks in advance.

I had some oil in the area where the pins are located. I removed the ECU and turned it upside down and sprayed CRC QD electronic cleaner and dried it with compressed air. Then, installed the pigtails. So far, it's oil free and still running like before.

What kind of symptoms did you have before discovered ECU had oil? Did you just prayed the connector or took the ECU apart? And did the faults just reset itself? Thanks.

I had no symptoms per se. Discovered the oil leak by chance when I was r/r the spark plugs on the left bank. I sprayed the connector.

Thanks. You’re very lucky. I tried to find a way to fix my ECU instead of taking it to the dealer for $$$$. I heard some shop would repair the ECU by mailing it in and they will clean and reprogram if needed. May worth the try.

Also, did you install the pigtail for the 4 camshaft magnets or the 4 sensors? And why not all 8?

If your ECU pins are drenched in oil, an engine hose down is a most.

Remove the ECU, and clean the contacts with CRC electronic contact cleaner. Clean the harness connectors with CRC as well.

Remove the top plastic covers (all of the ones easy to remove, air boxes can remain but make sure you cover the intake with a plastic bag, and a rubber band). Remove the bottom undertray (under the car)

Then clean the engine bay with Sonax engine cleaner (what MB uses to find leaks) and a tooth brush. Hose down with slow water, then use a leaf blower (not compressed air) a cheap electric one works great.

Then hand dry any hard to reach spots, then hit the plastic with Sonax plastic cleaner.

Once that is done, hit all electric connections you can reach with CRC electronic contact cleaner after unplugging each one.

If you are getting O2 sensor errors, you may have to clean their harness as well.

Thanks Madman. The car still runs, but with less power, that’s still a good sign I guess. I have all sorts of code for misfire, etc. I see some oil from 1 female connector the ECU, will spray it clean.

When our MB dealer suspected oil had gotten into the MCU (ECU), they replaced the whole unit with a reman... Might want to talk to a good MB indy in your area, as they tend to get more creative, and less spendy in their repairs...

I'm currently researching this pigtail thing and it seems to me that the pigtails do not stop oil from getting to the harness, the concept I think is you'd rather have oil in the pigtail than in the main harness and just change out the pigtails from time to time instead of changing the whole harness for $15k. However, the pigtail could have been specifically made to stop the oil from getting to the harness, that I'm not clear on yet.

I found Cam Magnet pigtails from dealership, this part number ( 271-150-0156 ) but have not found any for the Cam Position Sensors.

Does anyone know if the Cam Position Sensors need the pigtail fix like the Cam Magnets? If so, what are the part numbers for the Cam Position Sensors pigtail?

The MB harness solution (i.e.pigtails) works. Last month I opened one up and it's comprised of a copper male/female connector. The physics of this type of connection will not support capillary action. I am 20k miles into my installation and I have not seen any signs of oil in the sensors, cam solenoid, or harness.

Did you put pigtails on the position sensors and the magnets? I ordered pigtails for the magnets today from dealer part # 2711500156 but I cannot find any for the position sensors. The position sensor has 3 wires and the magnets have 2 wires so it would be two different pig tails.

That component is just a male/female pin connector.

I don't believe that there is a harness available for the cam position sensor.

The harness (pigtail) installs on the cam solenoid.

Was there oil leaking from the cam position sensor into the wire harness or was it only the cam magnets that was doing that? In any case the dealership told me today the previous owner of my 2013 S550 had to have the entire wire harness and a few other damaged components replaced because of oil seepage from either the cam magnets or the position sensors. They said since it happened once it'll likely happen again. I have no pigtails on the car now, so they just replaced everything and then didn't worry about the problem happening again.

I discovered oil in the harness at the ECM and took a shotgun approach and replaced the sensors and cam solenoids. Would you believe that it was very difficult to see the oil leaking from the solenoid connectors?