Code P0234
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Newbie
Joined: Mar 2017
Posts: 11
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From: Raleigh-Durham North Carolina
cls 550
Code P0234
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?
Super Member
Joined: Feb 2019
Posts: 681
Likes: 405
From: FL
2012 E550 sedan 2019 E63 Wagon
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.
Is you car going on limp mode? Could be a stuck wastegate or a bad pressure sensor.
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Joined: Apr 2016
Posts: 457
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From: Phoenix, AZ
2016 E350 Sport 2WD
Thread Starter
Newbie
Joined: Mar 2017
Posts: 11
Likes: 0
From: Raleigh-Durham North Carolina
cls 550
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.
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Super Member
Joined: Nov 2011
Posts: 973
Likes: 376
From: Austin, TX
2013 SL550 BiTurbo
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.
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.
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Thread Starter
Newbie
Joined: Mar 2017
Posts: 11
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From: Raleigh-Durham North Carolina
cls 550
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.
Super Member
Joined: Nov 2011
Posts: 973
Likes: 376
From: Austin, TX
2013 SL550 BiTurbo
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?
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Joined: Dec 2011
Posts: 1,273
Likes: 129
From: Orlando, FL
2015 GL550 4matic
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.
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.
Last edited by jonUF02; Jun 19, 2022 at 11:33 PM.
MBWorld Fanatic!
Joined: Dec 2011
Posts: 1,273
Likes: 129
From: Orlando, FL
2015 GL550 4matic
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.
Newbie
Joined: Mar 2022
Posts: 4
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2012 CLS550
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.
MBWorld Fanatic!
Joined: Dec 2011
Posts: 1,273
Likes: 129
From: Orlando, FL
2015 GL550 4matic
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.
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.
