Hi All,

As you may know, certain builds of the M271 (officially at least; I'd imagine ALL M271s are affected) have the cam sensors leaking motor oil all over the wires/harness. There is a TSB out for this.

MB has some kind of fix for this, which includes replacing the sensors and adding some additional wiring to isolate the problem.

For those who have had the TSB fix done, can someone please post ALL the part #s (and descriptions) off the invoice? I am looking at my invoice and am suspecting my SA screwed me.

Thanks!

2x 271-150-27-33 - Isolating wire
2x 271-051-01-77 - Cam sensor

The problem with the TSB is that it only references certain engine builds. Mine is 740 and the TSB only referenced 744 (or vice versa, I forget), yet ALL M271 use the same cam sensor, I had the parts department check other VINs to see if there was an updated part #.

So ALL M271 will eventually see this failure.

Please, if you're keeping your vehicle get these wires and install them. If you're under warranty they will not pay for them until there is a problem. The problem takes awhile to surface, and by then everything is coated in oil.

It cost $80 CND for both isolating wires, and installation takes 10 mins.

Okay, so here's a pic of my engine with the 2 covers off. Pic 1 shows the front of the engine. I assume the ECU plug cover is the one that is circled in red (you need to pull a handle to unlatch it, and there is a large "F" on top) and the cam sensors are the 2 things with blue/purple arrows. If this is incorrect, someone please correct me.

The ECU plug (ie other end of the cable) was perfectly clean, just as the SA said. However, it looks like nothing was added to the wiring itself. (See pic 2)

My bill said this:
2 271-051-01-77 Magnet
2 002-997-24-90 Cable Tie
2 271-051-00-32 Cover

That's good the ECU is clean, yet was it before you brought the car in? They probably cleaned it.

Looks like neither the isolating cable were installed nor the engine harness replaced.

I'd ask them to:

1. Check the O2 sensor connectors.
2. if there is any oil in those connectors, demand the engine harness and O2 sensors be replaced. Otherwise this is just a problem you'll encounter later on as the rest of the oil works its way out of the harness and ruins the sender in the O2 sensor connectors.
3. The isolating cable was probably not installed cause your engine build # does not match the TSB. Demand that they are, especially since the cam sensors are the exact same part # of the ones that leak, and will leak again.

Your Service manager will complain that he cannot install parts that do not match the TSB. That's when you get him to call the district manager and complain yourself, that its unacceptable to fix a part with the same part known to fail.

You're going to have to get confrontational for this to happen, they will not offer this fix themselves. MB has gotten very cheap, hoping to pass these failures along to the customer after warranty expires.

Good luck.

Thanks for your help!

How do I check the O2 sensors? (I don't even know where they are located in the engine bay)

The connectors for the O2 sensors are under the car.

Read this:
https://mbworld.org/forums/c-class-w203/206488-diy-m271-o2-sensor-replacement.html

This is why the majority of the oil that gets into the harness leaks into the O2 sensor connectors. Gravity is a wonderful thing, probably all that saves the ECU from becoming drenched.

At about how many miles does this typically happen? I was hoping I can squeeze a few more months out after the warranty expires in June.

Just thought of something, can someone post a picture of what the cam sensors look like when leaking. Then we all can squirt a drop of oil in the right spot and bring it in while under warranty and say that they are leaking. The new ones won't leak, right? Don't need the harness unless it already leaked.

My service manager has said he didn't see one till this year, yet now has seen enough. Seems to be becoming a common problem on the M271 and are showing signs of it after 4-5 years and/or 100K kms of driving.

The leak is through the connector. The seal inside the sensor breaksdown and leaks oil into the electronics that seaps out into the connector. There will be NO visible signs of a leak unless you disconnect the sensor and find oil in the connector.

Want it replaced under warranty? Squirt oil into the connector.
Want everything replaced? Squirt oil into the MAF, O2 sensors, ECU, crank sensor, ... enough so that it all fails.

I do not condone this.

WRONG the replacement is the same part number with no update. The part has not been fixed to not leak.

This is why slammer/Ed should be mad. They replaced the cam sensors only to have them leak again in 4 years. The isolating cable doesn't prevent a leak, it only prevents it from leaking into the engine harness. Instead next time it'll leak down the front of the engine and onto the belts!

Okay, so I called my SA. He said the tech did everything "by the book" and sure enough, my "build" of M271 was not on the list, which would explain why only the sensors were replaced. Apparently the exact cam sensors (listed under different part #) are also used on the M111, and they have the exact same fix! And yes, he agreed that ALL M271s and M111s will eventually suffer this fate.

The SA did say that they've updated part suppliers and that he hasn't seen them leak since (of course not, you just replaced them all this year ) I told him that's fine, but then if he's not going to put them in, I want it on paper that he's guaranteeing they won't. He called back and said if they were put in along with checking the harness, then it would be covered under warranty (ie it's too late for me since I already had it done); however, out of "goodwill" he'll try to get management to approve the special repair.

So if you are to have them look/diagnose the problem, do NOT walk out of the dealer without having them installed!

Whatever works, I just want to make sure this problem goes away. SA said he'll call me first thing tomorrow.

So MB knows there's a serious problem, but will not fix it under warranty if it hasn't happened yet but it will likely go very soon after warranty, certainly something to complaint to NHSTA about to campaign for a recall. Also, it makes sense for everyone that is close to the end of their warranty to put a drop of oil on their connectors, get the CEL on and then bring it in and have the work done, at least you would get 4 more years out of the car.

Certainly the least we should all do under our last days of warranty is check for oil in the connectors, if it's there, run the motor with cam sensors diconnected so it throws a code, then plug it back and bring it to the dealer for repair.

The cam sensor has not changed part numbers, so I wonder why MB only put certain build numbers on the TSB when ALL builds will be affected.

I know dealers are restricted to following the TSB, they cannot bill for the isolating cables unless the build number matches the TSB. Yet they cannot be foolish enough not to know the problem will resurface after the warranty expires, potentially creating a very bad costumer relationship for the future.

When the SM first told me what the fix was, I immediately asked "has the part been updated? will it leak again?" only to have him respond the fix is to replace with the exact same part. Great, all those cars that have been fixed will leak again. Beware the C-class on the used market.

Good job MB!

MB will fix it if you find oil in the connectors, yet most will not know to check it, and the only way to discover the leak is either:
1. CEL due to secondary O2 sensor
2. Oil consumption (indicating a leak)

I'd recommend to anyone that gets the "oil level low" message to check the cam sensors, that's where the leak is.

Okay, just made a trip back to the dealer. SA put it in for me, free of charge. 2-minute job.

2 271-150-27-33 Starter Line

The lines look like they were kinda designed last-minute by MB (or their supplier). Just a 15cm extension, with a loose rubber sheath over the wires that is slightly shorter than the plugs (ie it can slide around), probably to catch some oil.

Yup, he just popped the hood, folded the new lines in half, tucked them in, and zip-tied them. This can easily be DIYed, just be sure not to let the additional wiring touch the belts, it gets awfully close!

See pics for closeups.

i had the parts for a few weeks now, found the time to do it today, was on my 2004 C230 that is out of warranty, was some very minor oil seepage there. i am going to inspect the connectors on my 2005 C230 that is still under warranty tonight, i bought two sets of cables and 4 tie straps, here are a few pictures. the way i attached mine a little different than shown above, they clear the plastic cover just fine and are far from the Belt.

This is a great post. And this is My first post. I have a 2002 C230 Komp. 2 dr Coupe. Out of Warranty.

I just got my car back from the Stealer.
They told me my hole engine harness had to be replaced. They were going to charge me 2000 for the work. I told him forget it. On my service paper it says "camshaft magnet leaking pushing oil through engine harness" Im going to do the work myself.

To see if I get this right.
I need to buy the extension p# A271-150-27-33
Buy Cam sensor
Connect and zip tie them up. What do I do to reset the check engine light?
When it says camshaft magnet, do they just mean cam sensor?
Thanks for the help.

If you're the DIY-type (and have the right reverse-torx socket) you may be able to switch out the cam sensors as well. If you look at the thing, there are only 3 bolts holding the cover on. Might as well replace 'em if you're down there.

Be sure to buy TWO of the extension pieces, one per side

Check Engine Light - either the dealer or someone with the StarDiag computer can do that for you.

Camshaft magnet = cam sensor.

Welcome to MBW

But if your harness has oil in it you probably have to replace it also, hence the big expense of putting in a whole new engine wiring harness, otherwise the problems will continue. The extension is to keep new oil from dripping into the harness. One advantage of having the dealer do it is that if there is a recall they will have to re-imburse you. This is why it's key to go to the nhtsa website and file a complaint and also, since this messess up sensors, go to the FTC, I believe they handle complaints related to the Federal Clean Air act for motor vehicles.

is it possible that would be covered by the emissions warranty? 8yr 80k miles
i did check the sensors on my 2005 today, they were dry, since i had the parts, i installed the adapters.

I had the $12 vacuum hose leak issue. We fixed it. The CEL is still on. Does the CEL go off after a while? Or does the dealer/a mechanic have to do it?

I wonder if the CEL is on because of the cam sensor issue. I gotta get in there and check.

Glad to have this thread on MBW.

Hi everyone...just wanted to double check on something. (I'm about to deal with the PCV hose issue and this cam sensor problem)

Tonight I popped open the hood and unplugged the cam sensors to take a look and miraculously I did not find one drop of oil! 2003 with about 50,000 miles and not a drop. Thank goodness. But my question is...if I don't have any oil in the cam sensor do I still need to buy a replacement (since the replacement is the same exact part with the same exact fault) or can I just buy the extension lines?

Extensions alone are good enough. My SA mentioned the sensors are new and "shouldn't" leak but personally I'm iffy on that (shouldn't they have updated part #s? ) Only time will tell.

Thanks a bunch!

My car is at the dealership, again, and i have the leaking cam problem. The SA called me and said it would be 3700 dollars to fix. Am i screwed? if i add in those parts you guys are talking about, will that fix it? Please help

Dude, you have a different engine, and different issue.

A very good thread.thanks guys