Hey W212ers,
Longtime lurker on here as a prospective, “hopefully someday,” owner of an M278 E550. In my time on this forum, I’ve seen a lot of murmurings about the somewhat-common issue of oil residue in the engine harness, leading to absurdly expensive repairs. Fearing for the wallet of owners a bit, we've come up with a proven solution using Genuine parts. This one will be a bit lengthy, but I'll lay out all of the info for you as well as the resolution we've found.
How Does Engine Oil End Up in the Harness? What Can Happen?
As I’m sure we’ve all read here at some point, there’s been a lingering issue in which “new-generation” engines wick engine oil through the camshaft adjusters magnet (and sometimes even the camshaft position sensors) and into the wiring harness. Unless the electrical plugs and connectors at these points are inspected regularly, the issue can be pretty tricky to catch in its infancy. Most commonly, owners only discover that oil has run the length of the harness and into the engine computer via a host of fault codes for auxiliary sensors (such as oxygen sensors and ignition coils) suddenly appearing. In these instances, dealers were recommending a full wiring harness and ECU replacement as well as every auxiliary sensor that the harness connects to (as they, too, would accumulate oil as it made its way around the harness). The bill is consistently quoted somewhere between $10,000 and $15,000, and while the issue had initially seemed most prominent on M278/M157 cars, nearly every semi-modern, direct-injected Mercedes on the market is using these same leak-prone camshaft adjuster magnets and cam position sensors. As these cars are aging into a place where higher mileage is a real possibility, we’ve been relatively flabbergasted that Mercedes hasn’t acknowledged the issue at all.
Veterans of the M271 Evo, M272, and M273 engines will recognize that this sounds familiar and may even be recalling a WIS relating to this. You’d be partially correct; on the M271, M272, and M273, this very same issue was prominent enough under warranty that Mercedes developed a “sacrificial wiring pigtail” meant to trap oil leaking through the camshaft magnets prior to reaching the engine harness. Today, most vehicles with these older engines fitted likely already have had these sacrificial pigtails fitted early in life, and the simple wiring splice saved Mercedes a massive amount of money in M271/M272/M273 engine harness repairs.
The catch, however, is that the same issue currently occurring on the “late-model engines” (Anything using the M276-style camshaft magnets, which start in part number “276;” So M270/M274, M260/M264, M276, M256, M133/M139, M278/M157, M177) is happening outside of the warranty period. Despite the scale of the issue, Mercedes have given owners no path of resolution outside of replacing the full engine harness and accessories.
In the interest of finding a quick and easy solution that could save owners money, we found possibly the simplest solution of all. The very same “Sacrificial Pigtail” jumper harness that Mercedes made to stop this issue on earlier engines is compatible with current-generation engines and clicks directly into place without modification. For pennies in comparison, we have a fix for owners worried about oil running the length of their engine harness.
How to Inspect for Oil in the Harness:
To check for oil wicking in the harness, owners should inspect the electrical connectors at the Camshaft Adjuster Magnets and at the Camshaft Position sensors. If the wiring loom is inspected at the camshaft adjusters and the Camshaft Position sensor and no oil is found to be present, the owner can simply add the Mercedes Sacrificial Wiring Pigtail in these locations to prevent them from ever wicking oil into the wiring harness. Cars with one cylinder bank (M270/4, M260/4, M133/139, M256) will require two for the camshaft adjuster magnets and two for the Cam Position sensors. Cars with two cylinder banks (M276, M278/M157, M177) will require twice as many.
![Image]()
The Camshaft Adjuster Magnets on this M133 are circled; Cars with two cylinder banks will have four of these sensors.
In the instance that the Camshaft Adjuster Magnets are inspected and oil is found to be present at the connectors, we recommend the replacement of the Camshaft Adjuster Magnets (to stop the leaking at its source) as well as the addition of the Sacrificial Pigtails, to keep the wiring harness protected in the future. We’ve bundled kits for these as well, which include an electronics-safe solvent to blast the wiring harness plugs and get the residual oil out. There are kits for single-cylinder banks and for double cylinder banks in this instance as well. It would also be wise to add these pigtails to the Camshaft Position Sensors even though they are clean, in case they begin to leak in the future.
![Image]()
The Camshaft Position Sensors are again circled on this M133 to help identify them on your engine; cars with two cylinder banks will have a total of four sensors.
If the Adjuster Magnets are inspected and are found to be clean but the Camshaft Position Sensors show signs of oily residue on the connect plugs, we recommend replacement of the Camshaft Position Sensors (Again, to stop the leaking at its source) as well as the addition of a Sacrificial Pigtail, to keep the wiring harness safe. Once again, there are kits for single-cylinder banks and for double cylinder banks in this instance as well. It is advised to add these pigtails to the Camshaft Adjuster Magnets as well even though they are clean, in case they begin to leak in the future.
Quite frankly, this is a simple fix that anyone can do in their garage; simply adding the pigtails to prevent oil from reaching the harness will take a few seconds if you’re better with the fiddly connectors that Mercedes loves than I am. It's an absolute no-brainer.
Happy Driving!
-Danny
Longtime lurker on here as a prospective, “hopefully someday,” owner of an M278 E550. In my time on this forum, I’ve seen a lot of murmurings about the somewhat-common issue of oil residue in the engine harness, leading to absurdly expensive repairs. Fearing for the wallet of owners a bit, we've come up with a proven solution using Genuine parts. This one will be a bit lengthy, but I'll lay out all of the info for you as well as the resolution we've found.
How Does Engine Oil End Up in the Harness? What Can Happen?
As I’m sure we’ve all read here at some point, there’s been a lingering issue in which “new-generation” engines wick engine oil through the camshaft adjusters magnet (and sometimes even the camshaft position sensors) and into the wiring harness. Unless the electrical plugs and connectors at these points are inspected regularly, the issue can be pretty tricky to catch in its infancy. Most commonly, owners only discover that oil has run the length of the harness and into the engine computer via a host of fault codes for auxiliary sensors (such as oxygen sensors and ignition coils) suddenly appearing. In these instances, dealers were recommending a full wiring harness and ECU replacement as well as every auxiliary sensor that the harness connects to (as they, too, would accumulate oil as it made its way around the harness). The bill is consistently quoted somewhere between $10,000 and $15,000, and while the issue had initially seemed most prominent on M278/M157 cars, nearly every semi-modern, direct-injected Mercedes on the market is using these same leak-prone camshaft adjuster magnets and cam position sensors. As these cars are aging into a place where higher mileage is a real possibility, we’ve been relatively flabbergasted that Mercedes hasn’t acknowledged the issue at all.
Veterans of the M271 Evo, M272, and M273 engines will recognize that this sounds familiar and may even be recalling a WIS relating to this. You’d be partially correct; on the M271, M272, and M273, this very same issue was prominent enough under warranty that Mercedes developed a “sacrificial wiring pigtail” meant to trap oil leaking through the camshaft magnets prior to reaching the engine harness. Today, most vehicles with these older engines fitted likely already have had these sacrificial pigtails fitted early in life, and the simple wiring splice saved Mercedes a massive amount of money in M271/M272/M273 engine harness repairs.
The catch, however, is that the same issue currently occurring on the “late-model engines” (Anything using the M276-style camshaft magnets, which start in part number “276;” So M270/M274, M260/M264, M276, M256, M133/M139, M278/M157, M177) is happening outside of the warranty period. Despite the scale of the issue, Mercedes have given owners no path of resolution outside of replacing the full engine harness and accessories.
In the interest of finding a quick and easy solution that could save owners money, we found possibly the simplest solution of all. The very same “Sacrificial Pigtail” jumper harness that Mercedes made to stop this issue on earlier engines is compatible with current-generation engines and clicks directly into place without modification. For pennies in comparison, we have a fix for owners worried about oil running the length of their engine harness.
How to Inspect for Oil in the Harness:
To check for oil wicking in the harness, owners should inspect the electrical connectors at the Camshaft Adjuster Magnets and at the Camshaft Position sensors. If the wiring loom is inspected at the camshaft adjusters and the Camshaft Position sensor and no oil is found to be present, the owner can simply add the Mercedes Sacrificial Wiring Pigtail in these locations to prevent them from ever wicking oil into the wiring harness. Cars with one cylinder bank (M270/4, M260/4, M133/139, M256) will require two for the camshaft adjuster magnets and two for the Cam Position sensors. Cars with two cylinder banks (M276, M278/M157, M177) will require twice as many.
The Camshaft Adjuster Magnets on this M133 are circled; Cars with two cylinder banks will have four of these sensors.
In the instance that the Camshaft Adjuster Magnets are inspected and oil is found to be present at the connectors, we recommend the replacement of the Camshaft Adjuster Magnets (to stop the leaking at its source) as well as the addition of the Sacrificial Pigtails, to keep the wiring harness protected in the future. We’ve bundled kits for these as well, which include an electronics-safe solvent to blast the wiring harness plugs and get the residual oil out. There are kits for single-cylinder banks and for double cylinder banks in this instance as well. It would also be wise to add these pigtails to the Camshaft Position Sensors even though they are clean, in case they begin to leak in the future.
The Camshaft Position Sensors are again circled on this M133 to help identify them on your engine; cars with two cylinder banks will have a total of four sensors.
If the Adjuster Magnets are inspected and are found to be clean but the Camshaft Position Sensors show signs of oily residue on the connect plugs, we recommend replacement of the Camshaft Position Sensors (Again, to stop the leaking at its source) as well as the addition of a Sacrificial Pigtail, to keep the wiring harness safe. Once again, there are kits for single-cylinder banks and for double cylinder banks in this instance as well. It is advised to add these pigtails to the Camshaft Adjuster Magnets as well even though they are clean, in case they begin to leak in the future.
Quite frankly, this is a simple fix that anyone can do in their garage; simply adding the pigtails to prevent oil from reaching the harness will take a few seconds if you’re better with the fiddly connectors that Mercedes loves than I am. It's an absolute no-brainer.
Happy Driving!
-Danny
