moedollaz916

hey everone this is my first post but i need serious advice, im in texas i have a 2012 s550n 4matic , first it stated with a piston misfiring p304 code, so i thought it was the spark plugs, so i paid some bum mechanic 60 bucks to chnge them an he ended up messing up code 303 now also i got mad at him and made him tow my vehicle to mb dealership because he said he had to leave and the car was idling extrememly hard now, when i went to the dealership an they diagnosed it they said oil i engine harness, they said its 7500 to repair, car has 101xxx miles on it , i dont want to pay that much but is this a reason why the car would still be idling wierd an misfiring i feel like mb just wants my money now.

kbob999

Welcome to the forum...sorry to hear your troubles.

Here is my 2 cents...
To change the plugs, the mechanic may have removed the coil packs. If #4 coil got put in the #3 cylinder, the issue may have simply moved with the coil, or plug wires.

If me, I would find a better mechanic, then have him replace the #3 coil and plug wires, and see if the cylinder miss is fixed.
Then I would find the source of the oil leak and fix that.
Then I would clean the wiring as good as possible, and keep driving it like I stole it.
With over 100K miles it will have problems that need fixed, and depreciation has just about reached its limit. Stop driving when the cost to fix is too high.

Good luck, and keep us posted on the fix.

red996

Did the dealership visually show you the oil in the harness? If so could you please describe where you looked to see it? Where did the dealership say the oil was entering the harness?

Ninamashr

I've never understood why "oil in harness" would affect these cars this much? What is the wire insulating material made of, paper?

konigstiger

Common problem on 272/273 engines MBUSA released a Service Bulletin addressing the issue with adapters. Not aware of any releases for 278 yet.

chassis

The root cause seems to be failure-to-seal of the cam position sensors and cam solenoids. This means oil enters the connector, and is communicated into the harness by way of the connector pins. Capillary action brings the oil wherever it wants to go, and can go. One destination is the engine ECU, where the oil emerges from the cam position sensor wire, coats the pin in the ECU connector, and insulates the ECU from the cam position sensor. In other words, the signal from the cam position sensor to the ECU is interrupted. This leads to misfire and CEL.

The adapter harness field repair from Mercedes is evidently impervious to wicking, either by design of the connectors on the adapter, or by design of non-capillary wire.

red996

Excellent info. Thank You!