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My 2014 GL450 w/ M278 engine @ 61k miles came down with a check engine light recently. Dealer diagnosed oil leaking from cam sensors into engine wiring harness. Not clear yet how much beyond the sensors and harness they are fixing, they have to inspect I guess the other bits like ECU/injectors/O2 sensors. We'll see. Luckily it's all covered under my ELW, which just paid for itself.
But I am wondering for the future, in order to avoid this again is it possible to install the "isolation wires"/"pigtails" between the cam sensors and engine harness to prevent this from happening again in the future? I found there is a service campaign 2012070002 for some of the engine models just prior to the M278 that apparently share cam sensor designs with the M278, and the part of the solution under that campaign was to install these isolation wires. Just curious if anyone has done that to their M278?
Sound like standard rip off by dealership. How would leaking oil affect engine harness, which is designed to sustain harsh environment. Ask them for detailed diagnostics report - could be something else.
I had same **** excuse - oooo you have oil in wires - well gfy, reason for check engine was something completely different.
Sound like standard rip off by dealership. How would leaking oil affect engine harness, which is designed to sustain harsh environment. Ask them for detailed diagnostics report - could be something else.
I had same **** excuse - oooo you have oil in wires - well gfy, reason for check engine was something completely different.
I posted about leaking cam covers on my 13 GL550 not long ago. About the wire harnesses, what I found during my research was that there's a harness bundle and connector point near one of the seals, where leaking oil will get in and through capillary action work it's way to the other end of the harness and can short out whatever circuits are there... similar to flooded cars.
The piggy harness they came up with that's part of the fix is a sacrificial part so when the cam seals leak , it goes onto this piggy harness and gets directed elsewhere...a safestop kinda thing.
Reminds me...I still have to replace the seals on my cam covers lol.
OK guys, may be i am stupid, but oil is an isolator. It is not conductor like water. The only thing which could possibly happen is then plastic wire insulation got damaged with the time leading to the shortage.
Easiest solution would be spraying oil residue off with electric contact cleaner.
Now moneywise - on 278 it requires to take engine out to replace engine harness - one piece goes around engine. That is lots of income for dealership.
Sound lame, but one "professional" told me that cylinder head gaskets had to be baked on newer engines. To make things sound complicated.
The idea of the oil leaking and working its way through the harness does at first sound kind of far fetched, but there is actually as I said an official Mercedes recall campaign for this for engines prior to the 278. I am attaching the PDF. The issue seems to be the 278 shares these cam sensor parts with those prior engines and apparently at least in my car's case can still have this (very expensive) issue. So still wondering if anyone has taken preventative action steps of installing the wiring isolation system.
Check engine light came on last week on my '13 GL550 with 67K miles. Brought it to the dealer (I'm sill under CPO warranty). They found oil leaking past the camshaft adjuster solenoids into the engine wiring harness and ECU. They're still inspecting all the sensors that connect to the harness to determine which ones have oil contamination. They said they will be replacing the entire engine wiring harness and ECU + potentially other sensors. My concern is that the ECU also connects to wiring harnesses that go into the body of the car....i.e. CAN buses to interior, chassis, drivetrain, ABS, etc, etc. ...how will they even know if these harnesses are contaminated with oil? For those of you that had this repair done, have you encountered any problems thereafter with engine wiring harness or with other wiring harnesses in the body of the car?
Any updates on the fix/repair on the oil leak into the cams? My Gl550 with 40k miles is at the dealer and SA said leak is from camshaft cover. Waiting on what else may be affected after reading this post where oil infiltrated other parts.Updated with what was fixed
Leaking at right side cam gear cover
-reseal cam cover, replace cam solenoid seals. No more leaks after.
Turbo line seal on oil pan leaking
-replace seal for turbo inlet. No more leaks after.
Crush ring on drain plug for oil pan leaking
-drain oil, replace crush washer on drain plug for oil pan. No more leaks after.
parts list:
1 PKCAMCOVER 276/278 ENG CAM COVE WARRANTY
1 MB001-986-71-71-09 CLEANING AGENT WARRANTY
1 MB010-989-90-71 CLEANING AGENT WARRANTY
1 MB016-997-50-45 SEAL RING WARRANTY
1 MB000000-006365 HEXALOBULAR BO WARRANTY
1 MB000-990-95-06 SCREW W RND. H WARRANTY
1 MB003-989-98-20-10 SEALANT MB WARRANTY
#2 10MBZ DRIVEABILITY INTERNAL
CUSTOMER STATES COOLANT LIGHT ON ALL TIME
PRESSURE TESTED SYSTEM, NO LEAKS FOUND, CORRECTED
FLUIDLEVEL. TECH 1880
Qty Part Number Description Unit Total
1 MB278-181-05-80 METAL SEAL INTERNAL
1 MB007603-012102 RING,GENERAL,M INTERNAL
Update - the engine wiring harness had to be replaced due to oil ingress along with many sensors including fuel injectors. See attachments for complete workscope. I sure hope MB incorporated a design change into the new engine wiring harness at the cam position sensors to prevent this from ever happening again!
Hi, we share the same engine and google found this thread, so I thought Id post here before anywhere else. We have a 2013 E550 Sedan and took it to the Dealer for an oil change and to check on a TSB for the Timing Chain Tensioners. Car has 36K miles on it and was bought through CarMax (and thankfully we bought the MaxCare warranty). SA calls me last night and says warranty approved Tensioner job. BUT, same oil leak that you all are discussing he tells me is happening to our car (no CEL yet). They've turned the claim in to MaxCare since the estimate to repair has gone north of $10,000, and they aren't done diagnosing. MaxCare is sending an inspector out before they will authorize repair. Don't see why they wouldn't as their warranty is more comprehensive than CPO's. However SA said if they don't cover it he'll try to get the Dealership and/or Mercedes to "help"... Are you kidding me???! I'm out of town and told the Wife that when the warranty is up the car goes....
OK guys, may be i am stupid, but oil is an isolator. It is not conductor like water. The only thing which could possibly happen is then plastic wire insulation got damaged with the time leading to the shortage.
Oil being drawn through a wiring harness by capillary action, into a connector, and isolating the connector from making contact with its mate, is believable to me.
I have the M278 engine. My car was CPO and it happened first about 3 thousand miles out of warranty. $13k repair. I ate it because be the time they got to the problem the car was torn apart and I had not researched the problem. It was a panic decision. 15 months later, It is happening again. They sent me a $13k estimate. Supposedly I have a two year warranty on previous repair, but they have had the car 3 days and no word from Mercedes if they are covering it.
Is there a "pigtail" solution for the M278 like the M273? Or do I need to start replacing these parts as a maintenance item, and if so, which parts?
The root causes appear to be the cam position sensors and the cam magnets/solenoids. These are exposed to oil. They fail over time, and oil wicks into the harness and reaches the ECU and in some cases the O2 sensors. Misfires can occur.
Replacing the cam position sensors and cam magnets is the first step. If your ECU has been contaminated, it means there is oil in the harness. There is no practical way to remove oil from the harness, so a new harness is required if the ECU has seen oil. It's conceivable that ECU connector pins can be cleaned, and re-used with a new harness, sensors and magnets. But it's a guess.
If a vehicle is found to have oil at the ECU, the most conservative and expensive option is to replace:
- cam position sensors
- cam magnets
- engine harness
- ECU if exposed to oil
- O2 sensors if exposed to oil
This gives a clean starting point. If a vehicle is found to have leaking cam position sensors or magnets, but no misfires or CEL, the magnets could be replaced, and the harness connectors cleaned and observed as regular maintenance. This includes removing the ECU harness connector periodically to inspect for oil, and clean it if present.
Thank you. I guess my real beef is the the short time interval in re occurence. Are you aware if there is a "pigtail" solution for the M278 like they have made available for the earlier M273 etc?
No, I meant 276. But the 276 and 278 engines are closely related, so I would think the pigtails that already exist would work. You'd need to verify that.
This is what I have come up with. @LILBENZ230 are you positive the M271 jumper pigtails are compatible with M276? If that's the case I would say they work with M278, because M278 sensors have a "276" part number.
Can anyone with the pigtail jumpers please post a clearly focused, well lit photo of the harness connectors? This will help identify whether or not the pigtails can be used on M278.
Latest part numbers:
M272
Cam position sensor A 272 905 00 43
Cam magnet A 272 051 01 77
M278
Cam position sensor A 276 905 08 00
Cam magnet A 276 156 04 90
M276
Cam position sensor A 276 905 10 00
Cam magnet A 276 156 07 90
Where is the initial failure point, is it the sensor? Or the pigtail? Or a seal on the pigtail, I’ve taken the connectors off on my 2014 and don’t see oil. I get the traveling part of it just don’t understand where the original problem lies.
Where is the initial failure point, is it the sensor? Or the pigtail? Or a seal on the pigtail, I’ve taken the connectors off on my 2014 and don’t see oil. I get the traveling part of it just don’t understand where the original problem lies.
The cam position sensor and the cam magnets start leaking. They are exposed to oil and the oil travels from inside the engine, through the sensor or magnet body, into the connector and then through the harness.
The sensor body and magnet body is/are plastic. My view is that these black plastic injection molded housings crack in a location exposed to oil. It's an internal-to-sensor failure. The crack and leak may or may not be visible upon outside inspection, if the failure is recent or not severe. In a severe case, oil may be oozing out the connector.
Mercedes has a terrible reputation in my opinion for plastics that are barely suitable for use underhood. Barely suitable means paper thin and easily damaged, or the plastic resin degrades over time. This allegedly helps the planet by being biodegradable but owners are left with failed parts at low-medium mileage. Examples are intake ducts, vacuum fittings, radiator mountings, sensor bodies, the list goes on. Cost is also a motivator for MB, whereby use of thin gage plastic reduces plastic content and therefore cost to the manufacturer.
Summary: cracking of the plastic injection molded sensor/magnet body allows oil into the sensor/magnet interior, and the oil migrates to the sensor pins and into the harness. The pigtails are a field fix, not part of the problem.
I'm looking at the photos, and it looks the same, but that's just based on looks...
@Chedman13 the pigtails are cheap if memory serves. It’s a low cost experiment with potential large benefit to buy one pigtail and trial fit it on another engine. If it doesn’t work, throw it away or sell it on this site.
If it works, you’re happy.
The cam position sensors and magnets are commodity parts bin items that MB used across engines. The pigtails are simple two wire affairs. So low risk.
What may create a challenge for other engines is the local parts packaging situation and available space. For example on the M276 the intake manifold is nearly in contact with some of the position sensors, and fitting the pigtails in would be either tricky or not possible. This will be an engine-by-engine situation.
@chassis -smart thinking. Do you need to do the pigtails to your 2017 GLE350 or is this not an issue anymore?
I’m debating adding the pigtails. I check the sensor and magnet connectors once or twice per month. So far dry as a bone with 62k miles. I think by 2017 MB seems to have found something that works. EPC shows a large number of part numbers in the revision histories for these parts. This indicates to me they had a problem and were trying fixes.
The one challenge I am not quite happy with is that to install the pigtails in each position may require the intake manifold to be removed on the M276. Not sure if it’s worth the effort. Still mulling it over. If all pigtail positions can be installed on my engine without removing other components, it helps make the decision.
09-03-2019, 03:46 PM
