All:

I understand there's a known issue with the M278 where oil from a camshaft sensor or magnet can get in your wiring harness and fry your ECU. There seemsto be several fixes. One involves a pigtail adapter to extend the wires. What I don't understand is why this prevents the issue from occurring. How does this prevent oil from getting in the harness and thus the ECU if we're simply extending the cable? Is this a proper fix or a workaround?

 

There has been a lot written bout this issue. My thought has always been that, since this is a known problem, why hasn't MBZ fielded a fix for the affected series of motors?

 

Agreed. I'm trying to be proactive and fix it for $30 before I get hit with a $10K issue as I have 2 M278 vehicles.

 

Discard my question I found the answer. Fuuuuck. Good thing I checked, I have 40K on my car and sure enough one of the sensors or magnets leaked oil onto connector. God only knows what the GL 550 with 104K looks like. Ordered the pigtails wil also order replacement sensor or magnet.

 

MB did address the issue by creating the pigtails for the sensors and different sensors that come with a green o-ring, not black. I believe the pigtails are considered sacrificial, meaning they want us to check them every so often and if the pigtail is wet hopefully it will be caught before making it to the harness. The magnet pigtails are from EBAY seller zzperformance (only place to get them as MB did not make pigtails for the magnets from what I know). For all 8 pigtails (4 MB and 4 zzperformance) i think its about $100. I have two M278 engines and actually love them. Be aware of the Silitec vs. Nanoslide cylinder liners as well. Nanoslide replaced silitec, i believe it how it went.

 

As far as I know, Mercedes didn't have a campaign to install those replacement sensors and pigtails. The dealer has never mentioned anything about those when my car has been in for service. Is there a technical bulletin or similar that we can reference to the service shop?

 

What would we do without these forums and YouTube. Checked both my M278 vehicles. The S550 Coupe had a single camshaft position sensor leaking into the harness. But very mildly. Cleaned it, replaced sensor.

My GL 550 has 2 leaking camshaft position sensors. Again minor but cleaned them, parked it. One solenoid is also leaking oil but didn't wick into the harness. Waiting for the replacement sensors and solenoid.

Also ordered the pigtails for both. I'm amazed there hasn't been a class action for this issue. I'm not a mechanic but clearly the numbers indicate that anyone with an M278 engine WILL experience this issue. It's just a matter of how long before you notice or if and when it gets so bad you fry your ECU. Is there no way to build a harness that blocks out oil from a failed sensor? A Google search indicates MB isn't the only manufacturer prone to this issue. And the issue goes further back than just the M278.

It's been stated before but if you order from fcpeuro.com they warrant EVERY PART excluding fluid with a lifetime replacement (credit) warranty. So that should help reduce costs.

I've also set a 3 month reminder to check these sensors. I don't need a $15K bill from MB to replace a harness and ECU.

 

But not all of us are mechanics and have the know how and tools to do the work. I know that I have no idea where these leaking sensors are located nor how to access them.

 

I'm no mechanic either. But this is a major issue yet a simple fix. There are a ton of YouTube videos on the issue. It's matter of removing one bolt. The forums are here to help you.

EDIT
​​​I realized my post wasn't helpful to you. PM me I can do a quick walk thru with you over video chat and show you where they are and how to replace. Super simple and well within reach.