If you’ve been tempted by a depreciated Mercedes-Benz made in the past 14 years or so, you’ve probably wondered what could go wrong on them. As it turns out, many of them have a weird problem that owners are working around with cheap aftermarket parts. Owners are using sacrificial wiring harnesses to save their ECUs, and these extensions aren’t measures to guard against electrical gremlins, Believe it or not, they’re actually a bit of insurance against a truly bizarre engine problem. Let me explain.
The late 2000s marked the onset of downsized, turbocharged engines. While automakers weren’t necessarily reducing cylinder count across the board yet, a number of automakers shrank displacement and added turbochargers, and this strategy really took off in Europe.
Starting for the 2012 model year, Mercedes-Benz replaced its 5.5-liter naturally aspirated M273 V8 with the 4.7-liter twin-turbocharged M278 V8. Not only did this result in a substantial torque increase, it also slightly boosted EPA fuel economy, with the 2012 S 550 gaining one MPG combined and two MPG on the highway. While that all sounds great, the M278 did have a little issue with its new style of camshaft position sensors, one that could cause some serious damage if left unchecked.
See, these camshaft position sensors and cam magnets press into holes in the engine to monitor camshaft position, which means one end of each sensor gets intimate with the oily bits of the engine while the other is plugged into a main wiring harness that goes all the way back to the engine control unit. Unfortunately, the camshaft position sensors introduced on the M278 don’t always provide a good internal seal to keep the engine oil in the engine.
Over time, oil can push through a bad camshaft position sensor or magnet and find its way to the wiring harness pigtail that plugs into the cam sensor. From there, it can wick all the way down the main wiring harness to the ECU, causing some serious damage along the way. As you might expect, electrical components usually aren’t fond of engine oil, and some Mercedes-Benz owners have found out the hard way.
A cursory glance at the Benzworld forum reveals that this problem isn’t exactly rare. One owner of a 2013 S 550 reports that oil did indeed wick its way right down to the ECU, requiring replacement of the main engine harness, the ECU, and a litany of other parts. As the poster wrote, “Further inspection yielded replacing one high pressure fuel pump, three fuel injectors, and one O2 sensor at low, low, dealership prices.” The total cost of repairs is claimed to have run $7,000, and that’s actually surprisingly reasonable considering what others have been quoted.
This forum poster claims to have ended up with an $11,000 repair bill for the exact same issue, oil in the engine wiring harness. While it sounds like oil didn’t reach the ECU, it still seems to have taken out the ignition coils, fuel injectors, oxygen sensors, knock sensors, and the oil level sensor. That’s a lot of damage, and I couldn’t blame this person for looking at trading up to a Lexus LS after experiencing this sort of carnage on a 63,000-mile car.
It’s wild that this is even an issue, but the good news is that insurance against it is seriously cheap. This set of cam sensor harness extensions on Amazon will run the owner of an M278-powered Mercedes-Benz all of $25 and can be installed in minutes. Sure, you’ll need two sets to cover all the sensors and magnets, and they might get oil in them if some cam sensors fail to seal, but if caught early enough, it’s better to replace some cam sensors, magnets, and $50 worth of wiring harness extensions than a main engine harness and possibly everything in its path.
Mercedes and oil entering the engine harness…still happening on the newest models
byu/onepunchmeme inJustrolledintotheshop
Actually, this warning goes out to other Mercedes-Benz owners too. These exact same camshaft position sensors and magnets are also used in the later four-liter biturbo V8, the M270, M274, M254 and M133 turbocharged four-bangers in models like the GLC 300 and CLA 45 AMG, the M276 V6 in naturally aspirated applications like the 2012 C 350 and turbocharged models like the outgoing C 43 AMG, the M256 inline-six in the E 53 AMG and current-generation GLE 450, and even the 2012 to 2016 SLK 55 AMG. As this Reddit post demonstrates, leaky cam sensors are still causing carnage.
So, if you find yourself adding a non-V12 Mercedes-Benz made in the past 14 years or so to your stable, get a set of camshaft position sensor harness extenders ASAP. While not infallible, they’re a cheap safeguard against a seriously expensive potential problem.
Top graphic credit: Mercedes-Benz
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I feel slightly better about fixing my Fiat 500 trunk release by soldering a resistor into a Dodge Caravan part. They are externally identical but send a different signal to the BCM. Shrug emoji
So, the moral here is to buy the V12, right?
RIGHT?!
I can’t hear you as my ears were sold to pay for the $2000 coils, or the fact a falling leaf can kill them.
Wait, what?
Thanks for the PSA! At least there’s a cheap fix available. Better than the soy-based wiring harnesses prematurely degrading or attracting wire-gnawing rodents like they did back in the 90’s where the whole thing needed to be replaced.
I learned decades ago the very hard way that if you can’t afford a new Whizmobile 756SS, stay away from the used ones because in the long run, the new one will be far cheaper to own than the used one regardless of the initial entry price.
I have to keep track of the number of articles that highlight a hilarious potential failure mode that absolutely ruins a vehicle through catastrophic failure by country/manufacturer of origin.
Germany has to be number one.
The Koreans/Nissan probably are number two.
My rule for buying an older car is only buy it if it is for fun, or if it is used as a taxicab in some part of the world.
Sadly MBUSA doesn’t think taxi spec cars are good enough for us.
Is anyone doing modular wiring harnesses? Would be nice to just do a simple replacement of small sections as needed.
I mean, with a soldering iron and some heat shrink, they’re all modular.
Thank you. Without articles like this it’s a lot harder to resist the call of things like the magnificent E class wagon when we come across a seemingly good deal. You’re doing the world a service.
When I first heard of this issue years ago I thought what a strange issue. But I’ve heard of other brands suffering from this oil wicking situation in the mean time. The extensions seem like cheap insurance I guess you have to check your harness for oil when you check your oil.
I plan to do the financially responsible thing and only add V12-powered Mercedes from here on out. I’ll report back with how much money I’m saving on maintenance.
Make sure to get a least one non V12 model as a control for the maintenance savings comparison…
Yesterday it was your cooling fan is leaking and today it’s your wiring harness is leaking. Oh my.
Better than taking Stellantis and have your anus start leaking.
And they are worried about ads in bad taste.
Timely article since I was just posting about my flirtation with buying a 2018 E400 Benz. It’s a lot like a “scared straight” after school special about the dangers of German luxury cars.
Friends don’t let friends buy out of warranty German cars.
Also note VW warranties aren’t transferable to the second owner, so any used VW is an out of warranty German car.
The other rule of thumb is if you can’t afford a new German car, you can’t afford a used German car.
There’s a reason the modern ones depreciate so fast.
Every time I look at an old S-Class and drool onto my phone, I’m gonna reread this article again and it will slap me back into lucidity.
Maybe just look at even older ones, say, W126?
I like those too, but I’m pretty scared of the vacuum line issues on those generations. Don’t they use vacuum for everything?
I think if you block off the lines to the trunk and doors you should be good. Central locking is a pain anyway.
When I was in high school / college I had a 240D whose vacuum system was slowly going kaput – got to a point if you unlocked the trunk in the wrong way or used the air conditioning in the wrong – conditions – the engine wouldn’t turn off (and I think a couple of doors would just lock and unlock themselves for fun). Ever try to use the fuel-starving “stop” button on the top of a 240D engine to shut down a 240D engine? My hands are still shaking 30 years later.
I’ll bet it felt like mowing lawns all day with a gas engine.
The best fix is do the inspection services correctly (maintaining a car is not just changing the engine oil occasionally), identify that there is a leak, and fix the damned leak. You have to let it go for a pretty long time for it to become a major issue. FWIW, my car was more than 10 years old before one of mine started leaking. All four cam adjusters were replaced at that point. Not a particularly expensive or difficult repair. And a big reason I would never buy a car that was “maintained” at JiffyLube.
I guess the extensions are insurance, but I would not bet on oil not wicking right through them too, and it’s another connector to corrode or otherwise fail over time.
But oil leaks on my British cars are my rust protection.
Hey,
They’re just their marking their territory.
Cars like these aren’t designed to last more than ten years if you’re lucky. The makers truly don’t care. The issue is and will continue to get worse as they stop making replacement parts as well.
All cars are designed to last as long as you are willing to pay to maintain them correctly. <shrug>
Ha! Tell that to materials that degrade over time and systems designed as “maintenance-free.” There are many ways in which a perfectly maintained modern car can fail where the repair costs are greater than the value of the car.
The “value” of a car is more than what someone will pay you for it, in many cases.
And that is literally all cars. ALL materials degrade over time. There is no such thing as “maintenance free”. Sometimes maintenance means replacing. More expensive cars simply have more, and more expensive potential dilemmas due to added complexity. If the things that make a Mercedes worth owning don’t matter to you, buy something else. I find the juice well worth the squeeze. <shrug>
I saw the headline and my first thought was they were putting out cheese or something to distract the mice before they eat the wiring – which now often includes lots of soy in the insulation.
I would think someone should be able to expect that an expensive “luxury” car should be able to at least resist degrading for as long as some bottom end POS, if not longer. It’s one thing if it’s advanced features or tech that causes the problem (like the maintenance nightmare 600), but so many of these are baby steps engineering problems that low end marques selling low end cars at minimal profits with as much cost cutting as possible to not have parts fall off during a test drive seem to avoid. MB built a reputation on solidity and being built to last, but (for a while) now they’re just overpriced junk. Someone could pull an old LS out of a dead truck in a junk yard and get more reliability with less weight for the same power (or more) in a more compact package. There is so little value for the dollar with these, even if the doors shut nicely (something they did even when they made good cars and I wonder if the new ones are even as solid as a 300SL roadster). They are solid, so I suppose they’d make good getaway cars, but not if it’s beyond a few years old.
My comment was on the designed lifespan of the car. Not what is possible for people to achieve if they are willing to spend more on maintenance money than the car is worth. My point remains true. The cars aren’t designed to last. Especially premium brands, which are designed and engineered for an audience that keeps them for the length of the warranty and no longer.
Those are the profitable customers. The entire point is to make a less expensive product to lease than to own out of warranty. They have achieved that. It has zero to do with thinking a MB is worth extra money to drive. That is clear by the sticker prices. It is about the lifespan of them once they leave the lot.
I think you are right but still the brand has to take a beating when all the used car buyers crap on it and the resale value goes to shit. People didn’t get rich by being dumb. Unless they inherit.
The number one factor in a person’s wealth is the wealth of their parents, so…
But, I don’t disagree that many wealthy people are careful with their money. But that is kinda the point here. They don’t buy used cars if it doesn’t make financial sense to do so. They also don’t care what the people who need to buy used cars think. They also are less willing to waste time with dealers getting things fixed or doing their own maintenance. Their time is worth a lot.
If the car makers cared about the used market or those customers, they would care about depreciation. They don’t. The car makers don’t benefit from their cars being driven by “lower” classes because a big part of spending more for those brands is exclusivity. That is why they can charge a lot more for a “Competition Package” when most owners will never get near using the capacity of the regular model with the CP.
Car makers pick their customers more than customers select the car brand. The carmaker has all the data and research. Most buyers want something and then justify that desire.
Normally I’d kind of agree, but both of the cars mentioned in this article were dealer maintained, neither are high mileage, and this particular leak seems like it’d pretty difficult to detect. Sounds like run of the mill germancaritis to me.
Germancaritis – also known as a secondary definition of “krankenwagen”
Sort of, and I get what you’re saying, but ECU death by oil intrusion seems like something that leans more towards design defect than maintenance. If you don’t change your oil, sure, that’s on you. If your oil changes itself onto wiring harnesses *all other things being in good repair* that seems a bit tilted.