Hello everyone,

This is a cautionary tale for everyone with a SL550 that's more than a few years old....... The story I'm about to tell you may also apply to other R231 SL models but I don't know for sure.....

I'm not a very frequent poster here (last one was several years ago!). On background, I'm the original owner of a Black 2013 SL550 (purchased new in 2012) who has been enjoying the heck out of it for the past 8 years even if I don't drive it a lot. After 8 years, I only have about 36k miles on the car. I mostly drive it during the Spring, Summer and Fall.

Anyway, about 2 months ago, my check engine light came on. I thought the gas cap might be loose. That wasn't it. So, I took the car to a trusted MB mechanic (who works for a local dealer), and he informed me that the oxygen sensors in the car were leaking oil into my wiring harness and damaged both the entire wiring harness and bunch of electronics. Whoever heard of engine oil wicking its way through your wiring harness? Apparently, this happens to some MB cars.....

I had purchased an extended warranty for this car, but, alas, it expired back in 2019. Aughhh. The repair was MAJOR; they had to pull the engine and the transmission out of the car and replace the entire wiring harness along with all the sensors and some other electrical stuff. While they were at it, they also replaced the motor mounts and the transmission mounts as those are also prone to wearing out on these cars. They had the car over two weeks, but it came back to me in excellent shape.

I'll just say the bill was HUGE but MB Corporate stepped up and covered all the parts and a small portion of the labor - even though the car was fully out of warranty. I've been a loyal customer to the brand over the past 20 years (I also currently have a GLC43 coupe and a GLE 350), and they took that into consideration. All in all, I was satisfied with the outcome; they were fair. So, I'm still loyal to the brand.....

This is a cautionary tale; apparently these sensors can develop oil leaks over time and trash your wiring harness. So, when you have maintenance done on your SL550, please make sure to tell them to check all the oxygen sensors. Why they don't do this as a matter of course escapes me, but it is what is it.

I'm hoping my passing this on to all of you may be of some help.

See you on the road.....

 

There was a service update campaign issued by MB for the 'check engine light' staying on issue on 231's that was released back in April of 2019. It may apply to the model year you have, and if so, have this software update applied to your 231.

I had the 'check engine light' problem too, and like PilotMike, I initially thought it was simply due to a faulty gas cap. I promptly replaced the gas cap with a new one from MB Parts, and the problem did go away, but only temporarily. Just a few days later, the check engine light came back on again.

Doing some online research, I learned of the April 2019 Software Update Service Campaign related to the check engine light issues on early model year 231's.

Once I had my Dealer perform the service update required by the campaign, the problem was resolved and I haven't seen the dreaded 'check engine light' again.

So please make sure that your MB Dealer has performed the April 2019 recall service if you own a 2013 or 2014 SL 231.

Because this is a MB service campaign software update type of service, it is available completely free of charge from you local MB Dealer.

 

PilotMike, thanks for posting your ordeal and happy you got it resolved to your satisfaction. I don’t believe the outcome would have been so positive, had you not been the original owner and a loyal MB customer. I’ve read about this issue on another forum, I can’t remember which one. For others out there, do we know that this potential problem has been fixed on the later 231 models? I also wonder if it is unique to the 550 models or if it also affects the V6 cars. Konigstiger, are you listening? Anything on this problem?

 

I do not see any recalls in effect on R231s. Was it maybe only for the early (Spring 2012) MY '13 production?

 

I don't think any notification was ever made to Owners when the 231 'check engine light campaign' was announced in April of 2019. It was just a service Dealers would perform when a 231 came in for some other type of routine service. Can't say for sure if it involved checking any oxygen sensors or not. To the best of my recollection it was a software/firmware update to the car's computer. Don't remember if it was applicable to all models years up to that point, but it did apply to my 2013 SL 550.

Your MB Dealer should be able to identify that campaign and which models needed the service.

In the meantime, I'll try and find the MB campaign notice myself and if successful, I will post it.

 

NEWSFLASH:

OK, I found the 231 MB Service Campaign Bulletin for the software update released to correct the 231 Check Engine Light problem. It appears to cover all 231's produced between 2012 and 2014, and there are other MB models involved in this Service Campaign as well.

Click on the .pdf file below to see complete details for this service campaign and if you have a 2013 or 2014 231, ensure this software update has been applied. As previously mentioned, this is available as a 'free service' from MB Authorized Dealers.

You may wish to just print a copy of this .pdf file and take it with you when you visit your local MB Dealership to have this important service update work performed.

 

Oxygen sensors cannot leak oil into the wire harness.

 

You are correct. I was wondering how long it would take for someone to post that O2 sensors contain no oil and are inside the exhaust pipe/manifold. Get an old discard and open it up...

 

I was wondering how in the hell an oxygen sensor located in the exhaust pipe could leak OIL into the wiring harness. Something is fishy about this story.

 

If MB covered part of the repair obviously there was leaking oil into the harnesses from somewhere but not from the pre or after cat’s O2’s. It would be interesting for all of us to see what was the repair description ?

 

I think it is a different sensor, located close to the engine.

 

Oil was likely from cam actuators, this was a widespread issue in 2000s MBs. I had not heard of issues recently.

 

Could the leak be ABC related?

 

I've had the problem too. error code indicates it is the cam sensors located on the front of the engine. And when they fail oil is wicked back up into the harness. they can replace the sensors, which are inexpensive and easy to do, but apparently it is so common that the oil wicks back into the harness that they recommend replacing that as well. That requires removing the engine and transmission, and is an $8.5k job at the dealer, somewhat less at an independent. i chose to try to have it cleaned out as best as could be done by an independent, and replace the sensors rather than spend the money since my car now has over 105k mileage. the intermittent check engine light recurred and the sensors were replaced again over the less than a year since the problem arose. when it happened again the car seemed to run ok most of the time, light or no light, but on one occasion the engine timing seemed to fail and ran rough, so i had the second replacement done. since then the engine light has been intermittent again, but the engine has run without problem. until it doesn't of course.

 

Check this thread: https://mbworld.org/forums/mercedes-...76-owners.html

The oil wicking into the wiring harness is related to the cam sensors and/or cam position magnets. When they begin to leak (and they will), oil travels from the connector through to wiring harness and ECU causing $15-20k of required repairs. As a preventative, wiring extensions (sacrificial pigtails) can be added to the sensors and magnets minimize the risk of travel and making it easy to spot the leaking so the sensors or magnets can be changed. The extenders have open sections in the sheath (mitigates migration and makes it easier to spot leaking).

I checked my 2014 SL550 with 27k miles and 3 of 4 cam sensors were leaking. The 4 cam magnets were all dry. I am replacing all cam sensors and adding extenders to all cam sensors & cam magnets.

 

Could you share the behavior that occurred as a result of the oil working its way up to presumably one of the engine control modules? I had heard of oil reaching via the overhead cam position sensors but not the O/2 sensors and I'm getting random misfires on what was one cylinder then 2 then 4 and now 8. That smells of computer like failure to me.

 

I agree..

 

I'm surprised to see that newer SL's still have this problem. The software fix must be for some other issue because it obviously isn't going to fix an oil leak.

It's fairly easy to see if you have the oil seepage problem. Pull the connectors on the cam sensors. If you see oil inside the connector then you have the problem. The cam sensors and actuators are on the front of the engine and fairly easy to get to.

It takes a very long time for the oil to seep to the ECU. So if you see oil in the connectors it doesn't necessarily mean you have a major problem. But you definitely need to do something about it to prevent future headaches.

I had this problem on a 2013 SL that I no longer own. It only affected the sensors and not the actuators. I pulled the connector shell back and confirmed that the oil had not seeped into the wires. In my case I tinned the stranded wires at each connector pin with solder. I also replaced both cam sensors.

There are plenty of threads on this forum about the oil seepage problem.
.

 

Did you ever have any engine codes for random misfires, or misfires cyl x?

 

Thanks Joe,

I too did the same procedure you did. I proactively purchased new cam position sensors and sacrificial wire harnesses. Someone else mentioned that the O/2 sensors need to be added to the list for wicking. If they have been compromised, that could explain misfires if the ECM is getting invalid or no input from O/2 sensors. Although if that were the case, one would expect misfires on four cylinders and a related error code. My problem started off with 1, 2, then four and finally now 8 cylinders with random misfires. If anyone is familiar with similar, I would be grateful in the sharing of experience especially with a good ending. As I fear this is the end of my love affair with my SL taken from me too soon middle-aged at 85K miles.

 

My SL never had any symptoms. I checked and found oil in the connectors solely based on a post I saw on these forums.

There's other potential causes of misfires. Did you find oil in the connectors? I would start by pulling a couple spark plugs and examining them.

 

I also noticed oil residue in the camshaft position sensors on my 2013 350 I purchased 4 updated ones from MB . I now check them every service and they are free from any moisture of any description.
As others have said it's well worth checking them, and if you can do it yourself it's not an expensive fix.

 

So, does this mean that the SL450 will also have the same problem? Yikes!

 

Not nessaraly, later models will probably have the upgraded sensors. Someone on here might know.