I'm looking for advice on the M276 oil-in-harness issue for my 2014 Mercedes E350 (80,000 miles). I was performing preventive maintenance and currently have no check engine lights or fault codes.

My goal was to get ahead of the known oil wicking problem. What started as preventive maintenance has now become a concern that I may be too late.

What I Found:

1. I planned to replace the Camshaft Position Sensors and install the sacrificial pigtails/protection kit on the Camshaft Magnets (Solenoids).
   
2. The Camshaft Magnet connectors were clean.
   
3. However, after finding oil in the air filter housing, I inspected the four Camshaft Position Sensors (CPS).
   
4. All four CPS harness connectors were soaked in oil. - Video and Picture Attached called Camshaft Position Sensor with Oil
   
5. I immediately checked the main ECM plugs. The good news is that I found no trace of oil on the ECM pins or on the harness connectors at the ECM end. Pictures attached - ECM Plug A & B ECM Pins A & B
   

What I've Done So Far:

1. I installed four new OEM Camshaft Position Sensors.
   
2. I have been meticulously cleaning the male harness-side connectors (the plugs that attach to the sensors). For the past week, I have sprayed them daily with Liqui Moly Electronic Cleaner and let them air dry completely.
   
3. I believe the sensor-side plugs are now clean.
   

My Core Question & Concern:

My main worry is the oil I can't see.

I’ve cleaned the sensor end of the harness. But since the oil wicks inside the copper wire strands (not just on the outside), I am extremely concerned that a significant amount of oil is still trapped "in between"—somewhere in the middle of the wiring harness, slowly migrating its way to the ECM.

My dilemma is: How do I address the oil that is almost certainly still inside the wires, even if it hasn't reached the ECM yet?

• Should I button everything up and just religiously monitor the ECM plugs every few weeks, cleaning them with electronic spray if or when the oil finally appears?
  
• Or, is there any known method to flush or clean the harness 'in between' to get the trapped oil out before it travels any further?
  
• Has anyone been in this situation, found the oil, cleaned out the oil, and if any oil made it into the ECM, cleaned it and not have any codes, etc. afterward?
  

I'm desperately trying to avoid the catastrophic "$10,000 ECM and new harness" repair. Any advice on the best and safest next steps would be greatly appreciated.



The old Chamsaft Position Sensor

ECM Plug A

ECM A

ECM B

ECM Plug B

 

This is a tough question about "The $10k oil in harness" topic.

I am not sure there is a great answer to deal with this AFTER the fact - It is best to PREVENT heatsoaks AHEAD of baking all engine plastics.


You can add the exhaust sensors that are located low down the harness to the infamous PCM contamination.

Their failure materialize with CEL's.

Lambda use an "open-concept" so oil traveling down the harness right inside the sensor-chamber. Each new sensor gets contaminated from the old harness so you may want to install a "Lambda pigtail".

 

If you are really curious to see how far the oil seepage has gone up the wires, you can remove the wire insulator approx 15cm away from the camshaft position sensor.
But make sure you seal them properly after that.
With a mere 1 cm exposed copper strand, you can spray contact cleaner and let gravity feed the cleaning solution down to the connector.

If you peel all 3 wires, separate their position 1.5 cm apart, safer when re-sealed and less fat too.

I would not worry if I have not seen any oil trace at the ECM connector wire harness side and ECM side.
Be informed that the pins ( usually the female ones goes bad fisrt ) of the ECM has good life up to 50 insertion cycles if silver plated. So dont over abuse your ECM connector.
https://mbworld.org/forums/e-class-w...onnectors.html

Good luck....

 

I agree with S-Prihadi. If you stop new oil from coming from CPS it's unlikely whatever is on the harness will move towards the ECU. I would recommend to clean as best as possible and just keep an eye out for new leaks.

 

So, if I change the 4 CPSs as preventative maintenance, would this hugely reduce the chances of the above scenario?

 

I have three wires coming out of each Cam Shaft Position Sensor, for a total of 12 wires currently affected (at least until I check the 02 sensors). This is the same wiring harness that also goes into the exhaust 02 sensors. Is that correct?

To rub salt in the wound, you are saying the oil can keep flowing into the 02 sensors and ruin them? Does the oil then run through the 02 sensors, pool in the catalytic converter, and destroy them as well?

I just want ot make sure that the fix would be to add a sacrificial wiring harness to the 02 Sensors? I've been looking online but can't find a vendor that sells one specifically for my application, so I'm stuck on this for now. Any advice would be appreciated.

 

Ah, that's a good point, thank you for that. I hadn't really thought about the limited lifespan of the ECM connector insertion, but it makes sense. I'll start keeping tabs on the "cycle" of disconnections and connections and try to keep myself out of it.

 

yes, new CPS + Pigtail are an effective step.

 

Sorry, ap41563, I didn't mean to go on a different tangent, but this discussion might help others and myself down the road.

Would these be the parts for preventative maintenance?
https://www.fcpeuro.com/products/mer...SABEgLG3PD_BwE
https://www.fcpeuro.com/products/mer...SABEgLNlfD_BwE

 

No worries, you aren't on a different tagent. Those are the exact parts I ordered, and I thought I was replacing them preventatively. Although in my case, the Camshaft Position Sensors had already gone bad and were leaking oil into the wiring harness. However, the Camshaft Magents were okay, so I just added the wiring harnesses to those as a preventive measure.

 

There's got to be a line shared between CPS and Lambda circuits - Not the signal line then either side of the power supply: GND/+12VDC.

The Lambda pigtails are not super-popular until you are facing the $10k harness feeding oil non-stop into $100 Lambdas.
I've seen VW owners dealing with exact same leak issue where $10k repair was not an option.

You're not dealing with a river of oil, likely only 5mL volume.

Plan B may be to experiment custom sealing each of the lambda wire strands to preserve Lambdas contamination. Then experiment sealing the ECU male pins so oil won't penetrate the enclosure through the pins.

 

For M276/M278, wires or connector which can or may have oil in them when they get old, they are :

01. 4 x camshaft position sensor <----- I will replace mine by 14th year, now been dry. I won't use extra pigtail, the more interconnector exist, the more bad contact possibility.
02. 4 x camshaft magnet, the round black thingy <---- I have replaced all four like 3-4 years ago as preventive.
03. Engine Oil pump solenoid <----- Mine is diverted, thus its like sacrificial connector in place.
04. Engine oil level switch <----- For now I pray it wont wick oil , but I will replace it when I replace the engine oil pan baffle oil suction snorkle combo, latest by 2027-2028.

All these 4 locations are oil bath region. Thus the risk is high.
If say engine or its PCV is not healthy, if high piston blow by... meaning high positive crankcase pressure, the higher the chance of oil wicking thru them wires...pressure assisted.

 

Thanks, @S-Prihadi. Very good point about the Oil Pump Solenoid. I checked mine, and it's not wicking oil at this time. I am starting to think my PCV system may not be functioning correctly, which may be the cause of some of this oil wicking. I've decided I'm going to replace the pump because at this point I couldn't hurt and I'm close to getting at it now with the intake off.

 

You can suck the oil out of the wires if you want, like how I do. My sensors leak and I simply let them, and I don't need pigtails at all:
https://mbworld.org/forums/gl-class-...ml#post8771425

 

First post guys love theses type forums so much info and help. Anyway I have dug deep into this oil wicking business. I am a shade tree mechanic so bare with me. I have a 2014 e350 conv 43000 miles. all the sensors I could get to 3 aren't accessible until I remove the intake have been dry, so yeah for me. Here is my question I bought the eight sacrificial harness off eBay. Tell me why I can't cut those harness and solder in a solid core copper wire effectively killing capillary action or oil wicking. I would use the shrink wrap with the built in solder and glue that seals the entire unit. Will this being unshielded mess with the cam signal. I thought also about putting a slip on shield sleeve but it wouldn't be grounded. I have read of guys on older MB with this issue stripping the wires and just dropping solder in-between the copper strainds basically making a road block. Theses were also not shielded. Have no idea if this will work but chopping up 25 dollar harness sounds better than touching the actual harness.

From what I gather the sacrificial harness doesn't actually stop the oil wicking it just buys you time to catch it before it makes it to the main wire harness. Is this true or do they actually block the oil and after awhile you would just get a code on what ever cam sensor and say well time to change that sensor and buy a new sacrificial harness. I'm basically looking to completely block this oil and only worry about a cel telling me the sensor is done and just change a bad sensor.

Just bought this car for my wife she wanted a weekend conv down her in Florida. I just did the full trans fluid change that was fun (not). Then found out about the hydraulic lines for the conv getting pinched and leaking now this oil wicking ****. This car is killing my OCD which is bad I worry about this car constantly is this what being a Mercedes-Benz owner is like. Cause it sucks. But the car is immaculate and we love driving it.

 

Yes it does not STOP oil migration, hence the name sacrificial harness , you can catch early oil migration on that short wire kit, saving the main long harness.
To not have oil migration I think best is to replace all 4 CAM-POS sensors on regular basis. For high mileage guys, perhaps X miles.
Me low mileage guy, I would say 12 years or next year for my engine would be good. Mine super dry now, but only 44,000KM only albeit 11 years old.

 

The sacrificial harness might be cheap insurance to make sure wicking doesn't reach the ECU, but with vigilance. When replacing the sensors and magnets, are they plug and play? I can't remember where but I recently read a thread on a British forum where they said that camshaft might have to be in a certain position when replacing the magnets, I might be off here and not comparing apples to apples.

 

100% plug and play, no need to align anything on the camshaft.
But do remember the very low torque value on the magnets and non re-useable bolts (3) , which is aluminum.
The VVT cover is magnesium.

BTW I just ordered 4 new cam sensors for my car. 1 month special order. Good for 2026 refresh.
The part number never changed till now. But my magnet has gone thru few part number changes if I recalled.

 

I just wanted to update everyone on my progress with this issue. I talked with my shop and walked them through all the work I've done and had them verify my work. Much as I suspected, they agreed with me that one part that is frequently overlooked with the oil wicking issue is that the PCV System is not functioning correctly. In my case, I had several symptoms of this issue:

• Oil was in the air filter box when I opened it.
• The dip stick would pop up after a spirited drive.
• The Oil cap was hard to remove.

Despite these symptoms, at no time did anything show up in the codes related to the PCV system.

My shop checked the manifold pressure and found that the PCV breathing camber had collapsed, so it was replaced.

I am hopeful we on the other side of this issue now, but time will tell. I'll be checking everything related to this at every oil change going forward.

 

This makes sense because if there is no pressure how would the oil be forced up through the sensors. I've heard the pcv valve on the back of the motor fails often so this definitely makes sense. Did you have a hard time getting the oil cap off when the motor was only running or also when it was off. And it's crazy it would pop the dipstick up.

 

No DTC will be triggered if you have bad PCV system.
There is no sensor inside the engine to read that crankcase pressure ( PCV ) system.
What you can do is to test the crankcase pressure as routine maintenance, aside from visual inspection of too much oil in the intake system.
Read here : https://mbworld.org/forums/e-class-w...sure-test.html
The tool is cheap, under US$100 you can get it

The problem is for us MB owners, MB does not provide any data on what the crankcase negative pressure is to be.
So when your PCV system is healthy, note it down and use it as reference.

 

I hope your new PCV delivers improvements on most of your expectations.

New E350 stock M276-NA + new PCV is more than capable to swamp the intake plenum with flash-vaporized oil unlike the turbo M276-TT PCV system that separates oil out much better to recycle it. Less dirty intake valves on turbo engines.


The dipstick popping up is to provide additional pressure relief - That is a witness sign of high blow-by pressure. That's from piston rings leaking uneven compressions.


The working PCV diaphragm should help normalize the idle crankcase vacuum to open oil cap.

Is crankcase pressure linked to "oil-in-harness" ?
I'd say no but pressure help feed oil through cracked plastic CPS.

 

From my understanding, the PCV can fail in either way: by providing too much vacuum or not enough vacuum. My oil cap was hard to remove with the engine running at idle, and when the cap was removed, the idle would actually change, which was enough to condemn the PCV system. If I gave my M276 the 'old Italian Tune-Up' for just one run, I could pull over, and the oil dipstick would be popped up by about half an inch from its holder. After replacing the PCV system, I did try the 'Italian Tune-Up,' and the oil dipstick did pop up, but only ever so slightly—not nearly as high as in the past. I ordered a new O-ring for the dipstick and installed it today. It is incredible to me how much resistance the dipstick now has. I did a test run and pulled over to check, and the dipstick was still firmly in place.

I feel like owning an older Mercedes makes you into an airplane mechanic. You always have something to work on and replace, and sometimes you replace stuff that "isn't bad, but it's just time".