CLS 350 cdi W218 Limp mode Y77/1 Boost Pressure Positioner Fault ? Gearbox Conductor Plate?? | Engine (2024)

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  • Apr 28, 2022
  • #1

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Philo999

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Apr 28, 2022
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Monmouth
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CLS350 CDI W218

Hi everyone, I have recently purchased a 2011 CLS 350 cdi (bluetec) with the 7-g tronic autobox, with 113k after a break from Mercs for a while as leased a car for a bit - it is great to be back behind a three pointed star... BUT on a couple of occasions the car has gone into some sort of limp mode, wouldn't change gear, wouldn't kick down, however no warning lights on the dash, and I managed to get the car to drop a gear using the flappy paddles eventually. When driven again soon after no problems at all. It has once or twice 'clonked' a bit going into top gear, but by no means regularly. Otherwise the car drives really nicely.

I did a bit of googling and I thought the symptoms were suggestive of the Conductor plate in the 722.9 autobox being faulty - lots of posts saying these sort of issues and that the conductor plate could be removed and sent off to be rebuilt (rather than buying a new MB one at significant cost). I bought an OBD scanner with transmission module capabilities and plugged it in but no transmission fault codes! It does have a lot of other data regarding the transmission though so I think it is reading OK, however there is a fault code 'Y77/1 Boost Pressure Positioner Fault' on the engine fault codes. Did I completely misread the symptoms and would this Boost Pressure Positioner fault cause the limp/no changing gear at all symptom?

Any help would be much appreciated, I don't have a particularly local Indy to take it to. Thanks Phil

  • Apr 28, 2022
  • #2

Petrol Pete

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Hello and welcome . When was the transmission last serviced and by whom ?

  • Apr 28, 2022
  • #3

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zipdip

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Did the car with any service history,you bought it recently have you any waranty on it,I have found quiet often when a 7g box starts to play up there are no fauts shown,but I suggest you find a indy and do a ATF change on that gearbox,maybe go with whatever the indy suggests,which might be take the electroplate out of the box as it is right there while you have the oil change and he might clean it for you sometimes it is just very fine dust causing the problem,when you get the fault while running the car have you tried stopping switching off the car for a few minutes and then see if the fault has cleared,if it does it points to a gearbox service being needed.

  • Apr 28, 2022
  • #4

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Philo999

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Apr 28, 2022
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13
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Monmouth
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CLS350 CDI W218

Petrol Pete said:

Hello and welcome . When was the transmission last serviced and by whom ?

Thanks for the response, the guy I bought it from privately was a mechanic (general type garage) said he did the autobox service in 2021.

  • Apr 28, 2022
  • #5

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Philo999

New Member
Joined
Apr 28, 2022
Messages
13
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Monmouth
Car
CLS350 CDI W218

zipdip said:

Did the car with any service history,you bought it recently have you any waranty on it,I have found quiet often when a 7g box starts to play up there are no fauts shown,but I suggest you find a indy and do a ATF change on that gearbox,maybe go with whatever the indy suggests,which might be take the electroplate out of the box as it is right there while you have the oil change and he might clean it for you sometimes it is just very fine dust causing the problem,when you get the fault while running the car have you tried stopping switching off the car for a few minutes and then see if the fault has cleared,if it does it points to a gearbox service being needed.

Thanks - no warranty as a private sale (mechanic - there is a rule not to buy cars from mechanics isn't there?). Car has full MB history till 2020 and it had a engine and gearbox service from him in 2021.

  • Apr 28, 2022
  • #6

W1ghty

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Jun 27, 2020
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Sunny Essex
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E320cdi and CLK200

Is the boost pressure sensor a current fault ? Maybe delete it and see if it comes back ?

For the boost sensor problem , a free job of 15 mins would be to spray clean the inside of the exhaust back pressure sensor with carb cleaner . There is a small hole that can block up .

  • Apr 28, 2022
  • #7

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Philo999

New Member
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Apr 28, 2022
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13
Location
Monmouth
Car
CLS350 CDI W218

W1ghty said:

Is the boost pressure sensor a current fault ? Maybe delete it and see if it comes back ?

For the boost sensor problem , a free job of 15 mins would be to spray clean the inside of the exhaust back pressure sensor with carb cleaner . There is a small hole that can block up .

Thanks for that - where is the exhaust back pressure sensor located?

  • Apr 29, 2022
  • #8

W1ghty

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E320cdi and CLK200

Philo999 said:

Thanks for that - where is the exhaust back pressure sensor located?

Top right of the picture with the black wire going to it . 24mm deep socket , watch for the silver coloured washer below it . It may not help at all , but at least you will feel you have “done something “ CLS 350 cdi W218 Limp mode Y77/1 Boost Pressure Positioner Fault ? Gearbox Conductor Plate?? | Engine (4)

  • May 3, 2022
  • #9

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Philo999

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Monmouth
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CLS350 CDI W218

W1ghty said:

Top right of the picture with the black wire going to it . 24mm deep socket , watch for the silver coloured washer below it . It may not help at all , but at least you will feel you have “done something “ CLS 350 cdi W218 Limp mode Y77/1 Boost Pressure Positioner Fault ? Gearbox Conductor Plate?? | Engine (6)
View attachment 126397

Thanks very much, I will try that CLS 350 cdi W218 Limp mode Y77/1 Boost Pressure Positioner Fault ? Gearbox Conductor Plate?? | Engine (7)

  • May 4, 2022
  • #10

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Philo999

New Member
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Apr 28, 2022
Messages
13
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Monmouth
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CLS350 CDI W218

W1ghty said:

Top right of the picture with the black wire going to it . 24mm deep socket , watch for the silver coloured washer below it . It may not help at all , but at least you will feel you have “done something “ CLS 350 cdi W218 Limp mode Y77/1 Boost Pressure Positioner Fault ? Gearbox Conductor Plate?? | Engine (8)
View attachment 126397

Thanks very much, I will try that CLS 350 cdi W218 Limp mode Y77/1 Boost Pressure Positioner Fault ? Gearbox Conductor Plate?? | Engine (9)

  • May 4, 2022
  • #11

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Philo999

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Apr 28, 2022
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Monmouth
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CLS350 CDI W218

Update: I took the car to to my nearest Mercedes independent specialist and they have said that it needs a new turbocharger between £2000-£2500! I keep reading on other threads that there is a way of repairing the normally electronic component on the control side of the turbocharger. The garage were dismissive of this and said the only way of curing the fault was how to replace the turbocharger. Not quite sure what to do now I would like the car a lot but it's a big bill!

  • May 12, 2022
  • #12

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Philo999

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CLS350 CDI W218

Having read through many of the threads about the turbo actuator being the faulty part, I decided to go ahead and take it off and have ordered a replacement from turbo vanes. There was some oil in the intake of the turbo and the intake and breather seals seem worn so I will replace those as well as there seems to be a fair amount on you tube videos about wear of these being responsible for oil there. I did note that some folks advised to check and see if any play in the centre of the turbo vane bearing (??) and I reckon there is a little play... does this mean the turbo is on its way out?

  • Oct 21, 2022
  • #13

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Drpaul10

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Mar 16, 2017
Messages
13
Car
Cls

Hi this sounds very much like my problem today my CLS 350 CDI (2012 7G auto, 80k) behaved in an odd manner. It seemed to want to rev in gear/hold the gear and only changing up at 3000rpm+ even though I was only light on the throttle. It was as if you were putting your foot down a bit but I wasnt( rather than it changing up at under 2000rpm say). I then noticed there seemed to be no boost… the torque and pull was gone. I then pulled over, Switched ignition off and on again. Normal service resumed. Then few mins after it did the same thing. Revving up to 3k even though only lightly on throttle. Im then trying to force it to change up with the flappy paddle which it reluctantly did (but not straight away). Something just doesn't seem right and seems turbo and gearbox related. No engine management light illuminated.It last did a regen about a week ago which went without issue. I'm going to have to root out my old code reader. Anyone suggest a good code reading app (assuming there will be a code)? Ironically it's in for a service next week (independent) and I mentioned to him that it's due the gearbox fluid change (last one was at 40k). Surely it can't just be that?

  • Oct 22, 2022
  • #14

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Drpaul10

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Mar 16, 2017
Messages
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Cls

My code reader reckons P0471 (exhaust back pressure sensor), p0404 (egr control range/performance) and p0299 (turbo underboosting). From looking on some forums sounds like it's either the egr or the back pressure sensor which is the cause but we will see!

  • Oct 22, 2022
  • #15

W1ghty

MB Enthusiast
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5,791
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Sunny Essex
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E320cdi and CLK200

Drpaul10 said:

My code reader reckons P0471 (exhaust back pressure sensor), p0404 (egr control range/performance) and p0299 (turbo underboosting). From looking on some forums sounds like it's either the egr or the back pressure sensor which is the cause but we will see!

Clean the hole in the back pressure sensor for a quick free job first

  • Nov 6, 2022
  • #16

unclebuck

Active Member
Joined
Oct 19, 2016
Messages
338
Car
CLS 320 /08

It takes less than 5 mins to unbolt the back pressure sensor, the guys here can tell you about my issues and the fact it took me 5 mins to resolve it.

take it out, oce out spray some cleaner in there get a cotton swab and gently clean inside ( i did mine ) once it all looks clean replace.

Also clean up the egr valve next to it, doesnt take long lots of tutorials on this, use oven cleaner does the job great. some info in my threads.

Do these first before you spend any money, it doesnt take long to do and is an easy job to do, then take it out and see who it behaves.

  • Nov 6, 2022
  • #17

unclebuck

Active Member
Joined
Oct 19, 2016
Messages
338
Car
CLS 320 /08

Philo999 said:

Update: I took the car to to my nearest Mercedes independent specialist and they have said that it needs a new turbocharger between £2000-£2500! I keep reading on other threads that there is a way of repairing the normally electronic component on the control side of the turbocharger. The garage were dismissive of this and said the only way of curing the fault was how to replace the turbocharger. Not quite sure what to do now I would like the car a lot but it's a big bill!

new turbo for essex turbos £250... same turbo that mercedes use only it has mercedes stamped into the plate ... once again check my threads.

  • Nov 6, 2022
  • #18

unclebuck

Active Member
Joined
Oct 19, 2016
Messages
338
Car
CLS 320 /08

Drpaul10 said:

My code reader reckons P0471 (exhaust back pressure sensor), p0404 (egr control range/performance) and p0299 (turbo underboosting). From looking on some forums sounds like it's either the egr or the back pressure sensor which is the cause but we will see!

back pressure sensor... clean it up.. clean egr valve next to it.

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CLS 350 cdi W218 Limp mode Y77/1 Boost Pressure Positioner Fault ? Gearbox Conductor Plate?? | Engine (2024)

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