Mercedes S Class with oil in wiring harness what is the cause and correction? 

Do not let Discovery ruin this dynamic. Y'all are great as is.

Dave as a 30 year GM tech and 17yr Fleet tech , I am very surprised you have not seen this in your past. This phenomenon is quite common with GM connectors , oil wicking from sensors that are in a engine ,trans area where some kind of pressure build up is common place .Same as battery acid wicking down the cable from the battery to the starter . The need to change a completed engine harness on the Mercedes S Class is totally unnecessary , along with the PCM or what ever Mercedes calls there module . If the PCM is working to pick up the fault ,then it does not need to be replaced .Hopefully new update cam sensors and good can of clean will fix this guys issue . I Think every Dealer tech at some point or another has stumbled across a oil soaked connector while fixing another problem . Dave your old school thinking in a High Tech environment with your techs is very refreshing to me . That's why I and many like me watch your channel (Discovery show to come ) .

I love how he called the mechanic over that was working on it. That is a proper show of respect for another man’s work. This is one of my favorite channels.

This channel just gets more and more interesting by the day. You sure employ some great knowledgeable people Dave.

24 year Mercedes tech here. Not the first engine with this issue. There was a recall on all 272,273 engines too for this issue. Now seeing it in 276/278 next gen engines. Replace all 4 can sensors and cam adjusters, solenoids, blow out engine module clean pins and harness. Good to go. And yes also happens with 722.6 transmission plugs. Also used in dodge transmissions. Fun stuff. Made a lot of time and hours fixing these cars.

In Europe / Germany you can buy so called "Oilstop cables". It is a harness which comes in the middle of the affected cables to stop the capillary action in the wire.

I love when people admit that they don't know everything and are willing to learn, this clearly shows you are a leader.

Mercedes and BMW's are wonderful cars. They give you luxury and performance all in one package, BUT. It comes at a hefty cost. I went down this very dark rabbit hole when I purchased a used 2009 BMW 335i X drive. This car was everything I could ever want. I never had a car that so refined, so comfortable and will the power and performance to match. It was very neglected when I got it. I thought I could rehabilitate it. Long story short. It completely broke my spirit and drained my Bank account, just in parts. The lesson I learned, is that if you can't afford to be in a relationship with a high maintenance model. Just be happy with the trailer park Queen 😂

25 year tech and 6 year technical training course developer / instructor here. To illustrate this phenomenon: The O2 sensors no longer get their ambient O2 content through a hole in the sensor housing. Instead, the ECM/PCM produces a pulse current in the wiring to the sensor which carries the ambient air to the sensor. Any system that has a varying current can produce a variation of this pulse current which can facilitate movement of air (or oil) along the wiring. Capillary action will move it some distance, but not all the way to the control module. Add a bad PCV causing the crankcase to pressurize, and you exacerbate the problem.

That’s ridiculous that Mercedes would not recall such a huge problem like that great video

Love the way you treat your employees like family Dave! Great info & i fwded this video to my Mercedes buddies!

I've been a Benz tech for 30 years, and we started seeing this on the 722.6 five speed automatic, electronically controlled transmission a few years after they were introduced in 1997. It would wick fluid all the way up to the transmission control module, sometimes ruining them.

I work at the dealer, and we just do exactly what you said, replace the cam sensors, clean out the connectors spray out the ME and kick it down the road. Only if the oil is dripping out of the engine control module will we do a harness and a ME control module. What you guys have is not that bad. Also, make sure you check the connectors at the O2 sensors. They’re pretty common for getting oil in them when this happens. Good luck.

42 years working on Mercedes and most all German and Swedish. 34 years on my own. Dave and his new series on the Discovery Channel will bring a lot of good light to honest and respected independent shops across the nation. Cheers to you Dave, and all the good, honest technicians out there with integrity and aptitude.

Please keep the uploads coming. Love this channel!

You can thank the capillary action or affect. Surface tension of the fluid in small gaps will slowly draw itself through, something to that idea

I had a 2016 s550, it was a nice car. One day a service advisor told me that a replacement engine costs over 60k, he then said just wait until the turbos go out, that will set you back about 10k. I sold it the following week!

Capillary action! This is a common problem that needs to be caught and fixed before it makes its way to the ECUs.

Well, I’m glad to see it’s not just me that experiences these issues! I own and operate a 2006 International 9400i with a Caterpillar C13 engine. This engine has wiring harnesses that pass through the top of the engine to operate the fuel injectors and intake valve actuators. Oil intrusion into these harnesses is a known issue, and the oil will flow through the connector at the valve cover, into the outside harness, and then travel down to the ECM and destroy it. These intake valve actuators are not known to be ultra reliable, but any time a fault code for an actuator or injector pops up, I immediately suspect that it is not one of these components, but oil intrusion. It is almost to the point that these wiring harnesses are a maintenance item to prevent damage to the $6000 ECM. Thankfully these harnesses are very easy to replace, it takes about two hours to do both the internal and external, which includes putting a meter on the injectors and actuators to monitor their resistance. It cost about $1200 to do the job. I always whinge and moan about Caterpillar part prices, but I guess I said shut my mouth and be thankful I don’t have Mercedes engine (sneering at you, Freightliner!).

Your team is priceless. Experience is everything

Chances are you will not see or read this however I believe it’s important to genuinely complement a fellow human when applicable. Allowing others to see who you are has such a positive effect, you are being not doing. It inspires it encourages those of us who strive daily to be the best version of ourselves and build others up not hold power over them. You deserve every bit of personal and business success that you have worked for.

It is crazy how a liquid can wick its way through a harness. Great videos boys.

This is unfortunately a quite common issue with Merc sensors (crank and cam) and happens to many engines. So you replace all of the sensors and install oil-stop cables in between the sensor and the harness. Basically, this is a cable with a cut and solder point in the middle, which you can prep yourself. Oil cannot travel beyond the solder point and so no further contamination can happen. But the harness is still full of oil up to the ECU. If time and money is not the issue, you can remove the harness and put lots of brake cleaner in it and hang it to dry. This will essentially remove all of the oil and things are back to normal. But since after installation of the oil stop cables no more oil can enter the harness a thourough cleaning of the ECU connectors would most likely do the job. But open up the ECU nevertheless to check, if oil has already entered the housing. Remove with brake cleaner. Thanks for all of your great content and greetings from the other side of the pond (Germany)!!

Oiling Capillary through the wiring and of a long distance surprised me that good find and diagnosis 👍

Great info!!! Mercedes has had issues with their engine harness' for years! I used to work at a Mercedes dealer for years and used to replace the engine harness' plus sensors on a few models. Some models were more labor intensive than others. Dealer repair is replace engine harness, sensors, and ecu plus programming. When I would do side work on these cars and the issue was caught early enough. Replace the sensors that leaked and plug in an extension harness between the sensor and engine harness. This little sub harness was used a sacrificial piece to minimize the oil getting further into the harness. There is a 2 pin and 3pin extension harness available. Mercedes actually makes an extension harness for the Camshaft Adjuster Magnet that was used on the older m272/273 engines and can be used on the newer m276/278 engines.

The ability of liquids to travel through tight spaces against gravity is called “capillarity” and is just a technical term for wicking.

I’m an old power stroke tech, and I approve this diagnostic message. Seriously though, not the first time I’ve seen oil push through a sensor and travel up the harness, but the fact that it’s just splash oil permeating is pretty remarkable. Now for my PSA: USE FENDER COVERS!! I wouldn’t breathe near that car without blankets covering every inch of paint, chrome, or plastic molding I can see.

Most expensive parts I’ve ever installed. Aftermarket alternator was $500. The guy at the store was shocked. I told him it’s $1500 at the dealer.

Good to see your looking after the customers and great work from Dave and his fellow colleagues, great channel 🙌🏼👍🏼

u guys are awesome- I've been a motorcycle racing mechanic,/rider for over 40 years and love your common sense diagnosis that is seriously lacking in the automotive and motorcycle repair industry these days - alot of "parts replacers" but not alot of true "mechanics" anymore

I can confirm this was an issue for a work colleague who owns a Mercedes. Another work colleague works to fix cars in his free time. The nightmare stories he tells me about Mercedes and BMW are shocking.

Saw this alot working for cummins, mostly on M11 and N14 engine speed sensors, the pickup coils would start to walk out the end of the housing allowing oil to enter the sensor housing, it would then work its way through the harness to the engine ECU, and on into the module itself where the carbon in the oil would short out the board and fry the ECU. This is a common problem not specific to mercedes, many makes have similar issues, TD5 land rover injector harnesses are a very common one that i've come across.

Dave you have a great crew. Keep the good work.

Dave’s Auto Center has Dave as the experienced PROFESSOR OF SURGERY while he and his up-and-coming surgical residents ALL make “rounds” each day on their “patients” ( the cars ). These rounds are NOT to be missed by the medical students. RS. MD, FRCS Canada

Dave I absolutely love your shop and how your guys are when diagnosing any and everything you all do!!! Keep up the great videos love em all !!

Outstanding video and presentation.

Contamination harness.. Put it back together with the seals removed for awhile @ the ECM. Let it finish wicking the oil from the wire.. Each oil change unhook and clean the master connector several times . Tinker Love - Make some love to it:)

BMW tech here, we see this a lot with the N63 engine. Not oil but coolant will go thru connecting terminal for the thermostat and work its way into the Bank 1 DME and fry it. TSB is available for this issue.

I cleaned mine up, replaced the camshaft position sensors. Re-cleaned every week till no more residue in PCM, and it's been good for almost two years now. I keep an eye on all sensors that touch oil now. I did use small paint applicators to put dielectric grease at the base of PCM pins but have since cleaned it up. Wanted to see if oil was still wicking. I know the oil is still in the harness, but it had never set a code for anything either.

A Mercedes leaking oil? Impossible.

This also happens to motorcycles. The oil travels up the wires of the stator. It burns up the stator, rectifier, and sometimes even the connector.

Hello from the state of California. I love watching your videos. Full and short videos. Please keep them coming. I always look forward to the next video. I was introduced to working on cars since I was 8 by my dad and never stopped working on my own and friends' cars. Wish I was employed by a shop like yours. Great job on the channel.

I am a BMW hobby mechanic and this is a rare, but known phenomenon on BMW‘s too. Sometimes even the diesel low pressure sensor fails the same way and diesel fuel leaks into the ecu destroying it. It’s a really weird phenomenon, and I remember how stupid I felt the first time I heard about it.

Dave, great team you've put together. I have never heard of oil following an electrical current! Incredible!

I agree with Kyle, I have seen that a few times on transmission electrical plug connectors.

This is similar to what happens on the Land Rover TD5s… but with them it’s through the injector wiring (which is inside the rocker cover) and it ends up in the ECU which on the defender is under the drivers seat! It’s a capillary action thing assisted by the current I think.

Capillary effect. The stranded wire allows oil in, the oil is more attracted to the walls of the wire than it is to the other oil molecules. The oil slowly travels up the harness. We have it happen with bleach on our delivery trucks.

I work on 18 wheelers Dave. Love the channel bud. I know for a fact Cummins isx engines and Volvo Mack have the same issues. We always offer to clean the connections, but there is NO WAY to clean the oil out of the insulation, so keep that in mind. The module hasn't failed if the car drove in and codes dont return after being cleared / test drive ect. CRC electronic contact cleaner for the module, harness if issues return and definitely any or all oil sensors with signs of oil on them.

I am a electronics tech at a paper mill and everything around here is coated in something. Wouldn’t recommend the brake clean it might melt some of the connections or wires. Safer to use “contact cleaner”. Available at Home Depot or lowes or maybe even a good auto parts store. Good luck Keep the great videos coming

Hvac tech here. Not a car mechanic but still love cars and am obsessed with your channel, Keep em coming Dave !

Audi&VW has a similar issue with coolant migration threw the harness from the ECT sensor. Top level RU-vid technician work! Much luv&respect from Hawaii🙏🏽🤙🏽

Oil is supposed to be dielectric which in my mind it has to be heat related to wicking oil in the capillary sense. Thanks for sharing!!!!

Actually ! ! ! ! ! ! I have encountered this on two of the Fire Engines I was in charge of ! One was due to fatality oil pressure and one was a faulty coolant temperature switch ! Thanks for sharing !

This is why I like this channel. Keep up the good work

I soo wish you were in my area! I have a 2012 Mercedes-Benz cls550 4matic and it's hard to find many honest reliable mechanics that won't break the bank; great shop great mechanics great owner!

Let’s go! Another episode 🎉😁

My cls 550 did the same thing .

Howdy howdy from Tucson

Thanks Dave & co.! Now every time I'm under my hood, I'm going to be looking for oily connectors...just in case. It's an easy thing to check (don't necessarily need to check *all* of them) while you're already in the area.

I am a DC power technician and I absolutely see this happening good call

I was taught about this in school. It's called different things, but I was told "wicking" is one of the industry standards. Cool find!

Looking forward to the TV series.

Dave: This customer went 200 miles over his oil change. We need to rebuild the motor. Also Dave: This harness and ECU is no good from oil saturation. A little brake clean and the customer is on their way. I'm joking by the way. VW's are notorious for coolant wicking past the coolant bowl level sensor and making through the harness. The most cost effective thing to do is de-pin the wires from the ECU connector, run new wires through the harness and terminate a new connector. Must cheaper than replacing the entire harness. Keep up the great work.

Man! What a great environment to work in!

Early Nissan Pathfinders with the VQ35 had issues of the IAC Valve leaking coolant through the connector and wicking through the harness to the ECU.

I remember back in the early 80s a gm car came in with coolant leaking on the carpet from behind the dash. Must be a bad heater core right? Ha, turned out coolant temp sensor leaked and sent coolant up thru the wire into the PCM which was located behind the dash. Coolant was literally dripping out of the PCM. 😂

My New Favorite Channel! Ex. A&P Mechanic here, I love your Troubleshooting and Diagnosis. I have a 2007 Mercedes GL 450. I would love to see how to go about changing the Sub frame mounts on this truck, no info anywhere. I do know Mercedes had problems with their Subframe mounts rusting on their smaller cars but no info on their trucks. And of Course everything at Mercedes is kept Hush Hush, Super Quiet. Thanks for all your great video's keep them coming!

I watch you all the way from Kentucky. I myself enjoy the hardest jobs out there. Love the way you explain and define what you are doing to folks that may not know. I prefer to work on the 6.6 Duramaxs but any medium duty diesel is right up my alley. Have learned quite a bit from your videos and look forward to watching more of them! Keep it up and this guy is gonna get a awesome engine!

Landrover td5 enginge suffers from the same problem, where the oil will capiller up the injector wiring to the ecu. on the defender the ecu is under the drivers seat box and will start to leak oil inside the seat box.

The GM 3.6 has same issue, the oil pressure sensor fails, starts leaking engine oil into the harness. When oil reaches pcm, results in erratic random driveability issues. Thank you.

Dave, I love your channel! I am a technican myself for 36 years the last 21 working for John Deere, I have seen this many times and on farm equipment I have seen this happen with water as well! One time I found a couple teaspoons of water in a controller that had wicked up the harness.

I love the condition, cause, correction, confirm that’s awesome!!!!

That crazy this car oil in harness

I've seen this in an older benz but thru the transmission module

Thank you guys!! The videos are the best!!

Hello Dave and all you guys doing a great job! I've been a person who likes to services my cars, and I used to have a 2002 E430 and a great German mechanic once told me, "as soon as you car reaches 120k miles, change the adapter plug and filter". I never did that until the car had 180k miles when I had the experience of having ATF in the transmission computer module. I had to replace the module, clean the harness and replace the plug, along with other transmision services. The fluid traveled with "capilary" action from the bottom of the transmision to the top to where the transmision computer module is mounted... this was a blow mind lesson to me.

Capillary attraction. Cable tie it

Very common issue on the m157/ m278 engines.

Hey Dave i was thinkingnit was the breather clogged.. and oil took the least resistance up the sensor and out that wire (like a straw)..with help of electrical currentto push it through... BUT wow..good info..i can add to my cells. Thanks..for the great videos

This is crazy! Never have heard of this before. Salt/deicing chemicals,yes, but oil that's a new one!

It’s not from the current guys. Its capillary action.

God stop interrupting him man, you ask for him to give an expert statement then talk over him, rude and not bright.

Dave, you're doing great videos thank you.

Yes super common. The cam magents sometimes leak as well or the oil level sensor in the front of the engine. Sometimes the oil will go to the O2 sensors as well

All I can say to you Dave and all of your employees, SEMPER FI !

​@DavesAutoCenterCenterville - has built a shop with not only top shelf talent but also a team with a vibe that would make almost anyone want to work there. Looking forward very much to future videos guys! 👍

Car gods Fast n furious quote 😂 nice 😂

I work on submersible pumps and have seen this also. Our fix is change wiring in the tank above the oil level with crimp connectors and new wiring beyond that. Have seen water do this as well. It gets interesting!

I knew about coolant migration but didnt know about oil also being able to do the same, always in hindsight does everything always make sense

That’s unbelievable! Wild , I’ve never seen that in any shop before !

I worked for a MB dealer 4 20 years. The things I have seen would make your head spin. That 14 S550 cost about 115 to 125k if it's not AMG. You hav2 remember that if you can afford that car, 10 to 15k repair is a drop in the bucket. But MB should good will it for FREE.

Capillary action is whats its called guys . Wicking is a slang term . Love ya work

Thanks Dave!

Dave, its going to come back. The oil in the harness will still "weep" into the control unit. We deal with this a lot on MB, BMW and Audi cars at our shop. I wish you the best. And remember, that $10-$15K is dealer mark-up.

As an Electrical Engineer i would also recommend blowing the oil off of the wiring harnesses to clean out the LENGTH of the harness, inside of the casing, from the inside out, all of the oil in the harness. The wiring insulation is rated for oil but you don't want the oil in the harness wicking into the harness or electronic module.

That is called capillary action or flow and is related to the property of oil to wet a metal - stick to it and climb. Exactly the same is with coolant. Sealed connectors help even more with pressurizing the whole system. This is why harnesses sometimes have unsealed splices or interconnections for certain cables or staiess steel conductors.

Yeah we had same issue on our C Class. Dealer wanted a crazy amount of money to fix. Independent fixed for 1/3

Loving these videos and the tips I get to keep from them, keep it up!

I work at a Mercedes dealer and i have seen this quite often on c204 and others around that year with a 270 engine (and other patrol engines with sharing parts). Oil pressure will push the oil trough the electrical pins trough the copper wire inside of the insolation and make it up to the ECU. I have had cases where the ECU was actually filled up to the top with oil like a good 300Ml of oil came out😂.

I saw that on the 2 liter chevy engines in the Cavaliers in the 90's. Oil pressure sensors allowed oil into the harness