My 2012 CLS 550 engine light came on diagnosed as code P0234. I did a little research but I would like to hear from someone who actually experienced this. What exactly is the issue and how much is it going to cost to repair?

 

Hi,

Moving your post to the W212 for help from fellow members. Good luck!

Bob

 

I would start by using a obd tool app like Torque and seeing if you are overboosting.

Is you car going on limp mode? Could be a stuck wastegate or a bad pressure sensor.

 

https://www.engine-codes.com/p0234_mercedes-benz.html

 

it only shakes a little when it idles and then the engine light comes on. I've taken it to a respectable Mercedes Benz shop I've been dealing with for years and they cant seem to find any issues. They even kept it for a month and nothing. As soon as I got it, not even a week later, and the check engine light came on with the same code.

 

Thank you but I already had that information, I just wanted someone who has actually experienced it and what did they do to correct it,

 

For intermittent issues don't overlook wiring and connector pin integrity.

 

have you logged it to check what boost pressure is being reported? Could be a faulty wastegate controller or bad module... or a cracked turbo housing or a damaged wastegate flapper, or many other things...

you said you just got it. Do you know if it has stock turbos? if they were upgraded, then the seller removed the tune, could be a genuine overboost condition.
Stock turbos for M278 are garrett mgt1752sm. AMG turbos for M157 are Garrett mgt2260sm. One of these numbers will be stamped into the id plate on the cold side of the turbo.

 

I havent recently bougt the car, I've owned it for well over 3 years and I dont drive it alot but I do drive it, especially on the high way. I would think everything you mentioned the car shop I've taken it too would have checked all those things out. By the way,they only deal with mercedes vehicles. So after hearing everything you guys have posted, maybe I need ro bring it to a couple more shops.

 

Sorry, I must've mixed up two different threads.

Yeah, unfortunately with random issues like this that are uncommon, it takes more to diagnose. Where are you located? Maybe someone in the same area can suggest a shop for you?

 

It’s been a while… but, what did you find regarding the overboost condition?

 

Looking for a resolution to P0234 code. I have a new to me ML63 with M157 throwing this code. I don't see many instances of this code.

Note: car seems to run just fine. I'm looking to figure out what sensor trips this. So far I'm seeing the MAP sensors in the air box, or the one that's actually on the intake manifold, under the wiring loom.

I'm using a good scan computer to read the boost level, which there is only 1 data value I see for boost, although the code P0234 indicates "turbo 1". The boost seems to go up and down normally with throttle.

 

I thought I would post some follow-up here regarding my last post. This code I believe was caused by oil in the engine harness from the cam sensors and adjusters. This is a common problem especially with M278 and M157. I found oil in the connectors of my 4 cam sensors and 1 adjuster. I also found a bit of oil on the ECU larger connector. I cleaned all this out with electrical cleaner and I've been driving for a week without the code returning. I ordered new sensors and adjusters. I will clean out the connections on both sides again when I replace them. There was already a good amount of oil back in one of the cam sensor connectors when I checked again yesterday. I had already changed these on my GL550 at only 60k miles I was seeing oil in the connections but no errors. I truly believe that MB is well aware of this issue, but they have not recalled anything. There are some extensive threads out there where people are told they need the entire engine harness replaced for this issue, a very expensive engine out job. I really hope that installing the new sensors and cleaning all the connections will keep any further problems at bay. I'll definitely be checking them regularly.

 

That’s rough thanks for updating. I have the overboost code pending that occurs when idling. Noticed a feeling like strong wind hitting the vehicle in park without increase in RPM’s. Plugged the OBDII in and saw the code. Hasn’t tripped the dash light yet, but it’s a 10-year old car with 100k where the game is preservation > rehabilitation. Aware of the harness concern and agree MB has to know. I checked the sensors 5k mi ago, and they’re dry. I’ll check again and see if that’s it. 2012 CLS550 btw.

 

Second update, after some more driving, the P0234 over boost code was coming back frequently. Engine harness was clean of oil, checked a few different times at the ECU and sensors after changing my leaky cam sensors.

The previous owner of my ML63 had chopped out the center muffler, which also acts as sort of an X pipe, mixing the exhaust paths between banks. After finding the correct part from Ebay I had that welded back in. I didn't like the loud exhaust to begin with. After restoring the factory exhaust path I cleared the P0234 code and it has not come back in a few weeks of driving. I believe this removal of the center muffler was messing with the back pressure on the turbo and causing the error.