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I have a 2012 E550 with M278 engine. My mechanic found oil in the wiring harness and He tried to clean it multiple times but still couldn't resolve the problem. He told me I need to replace the wiring harness. How much is the wiring harness? What about the labor cost?
Sorry, I have no idea what they go for new but it can't be cheap. You could try to find a used one on eBay which would probably be exponentially cheaper. Contact the seller ahead of time to confirm it doesn't have the same problem. I can look for the part number in EPC if you need.
If there aren't any problems you might be safe just leaving it alone assuming you have those small magnet harness extensions that stop the oil harness problem. I have some spares I could send you for the cost of postage if you want.
Parts cost for a new harness is surprisingly palatable in my view. Dealer or Indy labor to do the work is expensive. If you DIY it is doable and saves $$.
Cam position sensors and cam magnets are the root causes, change them now.
I contacted a well known supplier who is not sponsoring this board, but has been positively mentioned numerous times on it. They sell a kit of four of these addressing this problem. Their site guidance does not specifically state that these will fit a US 2013 E350 (M276) gas 4matic. So, I asked them, After providing my VIN, they said that they would not fit.
Yet, people on this board have apparently installed them, they fit, and they worked.
The sensors and magnets are MB parts bin commodities used across 4 engines: M274, M276, M278 and M157. There is a reasonable chance the mystery parts you refer to fit, if they look like the right part. The real question is will they, or won't they, leak?
from what I've followed, if the oil is just starting to travel up the harness from the cam sensors, you can probably get away with the new fixed cam sensors and not swap the harness for some years. If the oil has traveled all the way through the harness to the PCM, you're into deep doo-doo territory. regardless, any oil in the harness WILL eventually eat away at the insulation and cause harness problems, but that might not be for 10+ years depending on usage patterns. This applies to M276 and M278 engines, I'm not sure if any others are included. Once the internal insulation of a complex wiring harness is compromised, you will get all kinda random symptoms, and until the bad wiring is replaced, the car will just get worse and worse.
now, my experience with older Mercedes that had harness problems (<cough>1993-1997 M104 I6 engines, used in E320's and others over those years</cough>, as time moves forward, it becomes harder to find new/good harnesses, but there's a window when there's a fair number of recycled used 'good' harnesses on the market from wrecks and such. Those 93-97 M104s suffered from biodegradable insulation, and they still crop up on low mileage garage queens that are put back in daily service. cars that were being driven regularlly typically got new harnesses from the dealer in the 98-2000 time frame when the problems surfaced. This oil leaking from the cam sensors is kind of a different class of problems, however.
I think Mercedes released the updated cam sensors that don't leak somewhat before the W212 ended production, but I'm not sure what year that is. I have a late 2016 and I *think* its immune. I'm willing to bet that oil leaks are dependent on how hard you drive the car, but the oil pressure is typically pretty constant anywhere above idle so even someone who babies it might still get into these problems.
this is one of those m104 harnesses that was cut open to expose the bad wiring. note that NONE of this was visible before the outer sheath was cut away.
the oil damaged wiring will have a different failure mode, but I think you get the idea.
funny sub story. before I got into Mercedes by way of W124, I was a big fan of the older Volvos, 4 cyl RWD 240, 740, 940 Volvos up to about 1995, the cars were tanks, very simple and easy to work on and extremely durable cars. adequate but not much horses (my 740 Turbo Wagon had a 2.3L cast iron I4 turbo that was 160 horses, and 200 ft-lbs, it moved adequately, but wouldn't win any races, the non-turbo B230F engine was like 115 horses or something). Volvo adopted RoHS insulation circa early 1980s, and didn't catch and fix it until mid year 1987 (4-5 years later)... Mercedes had the exact same problem a decade later (93-97). Sad. While Volvos are of course Swedish, they had a LOT of German heritage, including extensive Bosch electrics. I've never swapped a wiring harness on a M276, but the M104 was probably an easier job than the Volvo B23F(T) engines of those Volvo 240/740s, even tho the engines on the Volvos were simpler. The key to any engine harness swap is to untangle and lay out the new harness on your garage floor approximately like the old one is in the car, then 'drape' it over the engine lined up with the old one and matching all the connectors, then start at one end and swap the connectors, extracting the old one as you go, then secure the new one in the cable trays and runs. In the 80s/90s, Mercedes used very high quality round pin silver plated and soldered connectors, that were all rebuildable. Nothing I've seen on my W212 leads me to think they still do this, the connectors are all crimped, and use all kinda wierd pins. the old 124's, almost every connector had some mix of 2 sizes of these silver plated copper round pins that were soldered onto the harness wires.
(late model B230FT in a 1992 740 Turbo somewhere north of 250,000 miles and still going strong)
Cam position sensor and cam magnet leaks affect M274, M276 and M278. This is entirely fixable if caught early enough. I check connectors for oil at each oil change.
Root cause appears to be a defect related to the injection molding design of the cam sensor body. @crconsulting did a great investigation into this by cutting open known leaky sensors. Oil enters the cam position sensor and is wicked into the connector and up the harness. To me it is not 100% clear how the oil enters the sensor, but @crconsulting 's work has been the most informative to date.
p.s. the common thread across many car manufacturers with regard to electric/electronic components, as mentioned in the previous post, is Bosch. Bosch flies under the radar because they do not have a direct consumer-facing relationship. The car companies handle the consumer. Bosch is the company that engineered and manufactured the DEF/DPF VW Dieselgate and MB Bluetec systems of worldwide fame.
04-14-2022, 04:32 PM
, as time moves forward, it becomes harder to find new/good harnesses, but there's a window when there's a fair number of recycled used 'good' harnesses on the market from wrecks and such. Those 93-97 M104s suffered from biodegradable insulation, and they still crop up on low mileage garage queens that are put back in daily service. cars that were being driven regularlly typically got new harnesses from the dealer in the 98-2000 time frame when the problems surfaced. This oil leaking from the cam sensors is kind of a different class of problems, however.
