Intermittent 722.9 P0778 Presure Control Solenoid "B" Electrical Code
Thread Starter
Junior Member
Joined: Nov 2018
Posts: 66
Likes: 5
From: Chicago
CLS55, CL63
Intermittent 722.9 P0778 Presure Control Solenoid "B" Electrical Code
I have been getting this code on cold start on my 722.9 7 Speed
I am also getting "Blind Spot monitor Inoperative" which seems to be in conjunction with this code- although it is possible it is separate.
The car is stuck in 2nd gear and in limp mode. Shifts to R and back to D are harsh, the coast is "sticky"
But if I drive around the block for ~5 minutes, and restart the car, the code is gone, and the car shifts perfectly for the rest of the day.
I recently replaced the TCC solenoid on this transmission.
Anyone else have this issue? The obvious first step is to drop the valve body and replace the PC solenoid, but as the code says "electrical", I'm skeptical.
I am also getting "Blind Spot monitor Inoperative" which seems to be in conjunction with this code- although it is possible it is separate.
The car is stuck in 2nd gear and in limp mode. Shifts to R and back to D are harsh, the coast is "sticky"
But if I drive around the block for ~5 minutes, and restart the car, the code is gone, and the car shifts perfectly for the rest of the day.
I recently replaced the TCC solenoid on this transmission.
Anyone else have this issue? The obvious first step is to drop the valve body and replace the PC solenoid, but as the code says "electrical", I'm skeptical.
Super Member
Joined: Feb 2007
Posts: 613
Likes: 296
From: Republic of Texas
W203 W212 W211 R53MCS
Replace the TCU (conductor plate). That's it. Highly recommend you get a new remanufactured unit from the dealer and not these fake reman units being sold everywhere.
Super Member
Joined: May 2002
Posts: 540
Likes: 39
From: Suburban Washington DC
1995 S280 5-speed
Assuming it's NOT the pressure solenoid referenced to in the code, it's most likely the TCM which is part of the conductor plate. I bought this used one on Ebay a few weeks ago that they program to the VIN, https://www.ebay.com/itm/275408182185 The first one they send threw some codes, but after contacting them about it, they were very helpful to assess the situation and shipped out a second one the next day. That one eliminated all the codes and limp mode I was experiencing. I just have a 3-4 upshift flare when cold now, but that's not related to the TCU.
Newbie
Joined: Sep 2023
Posts: 8
Likes: 2
From: Mountain View (CA)
2011 W212 E350 4MATIC Wagon
Hi! you seem to have the same problem as me. Did you observe any metal dust when you worked on your transmission? did the issue happen more frequently with time?
Link to my post where i explain my problem
Link to my post where i explain my problem
MBWorld Fanatic!
Joined: Aug 2014
Posts: 5,322
Likes: 1,678
S500
the Merc 7g gearbox operates on black tar and metal filings - one of the worlds worst gearboxes... if you find anything else something is wrong or it has just had maint work
on the conductor plate there are two 20 cent speed sensors that die around the 7 to10 year timeline - one dies frequently and is replaceable (by an expert) the other is unobtainium
the solenoids do the gear changes (controlled via the conductor plate) and are often in a bad way due to the swarf and debris of the self destructing bearings, clutches and box internals
fitting a secondhand conductor plate will mean the adaptions are set to the inside of the original box and is not a good idea - if getting bad changes tie down or flare up - if adaptions are not reset, or manually set up (by and expert), to suit the current box you will destroy whats left of its life
on the conductor plate there are two 20 cent speed sensors that die around the 7 to10 year timeline - one dies frequently and is replaceable (by an expert) the other is unobtainium
the solenoids do the gear changes (controlled via the conductor plate) and are often in a bad way due to the swarf and debris of the self destructing bearings, clutches and box internals
fitting a secondhand conductor plate will mean the adaptions are set to the inside of the original box and is not a good idea - if getting bad changes tie down or flare up - if adaptions are not reset, or manually set up (by and expert), to suit the current box you will destroy whats left of its life
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Thread Starter
Junior Member
Joined: Nov 2018
Posts: 66
Likes: 5
From: Chicago
CLS55, CL63
Hi! you seem to have the same problem as me. Did you observe any metal dust when you worked on your transmission? did the issue happen more frequently with time?
Link to my post where i explain my problem
Link to my post where i explain my problem
I have a STAR system so I can reset the adaptations without issue.
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Super Member
Joined: May 2002
Posts: 540
Likes: 39
From: Suburban Washington DC
1995 S280 5-speed
Sounds like a valve body issue. When cold the fluid is thick and causing a valve to hang up. When warm the fluid thins out and the valve moves normally.
Newbie
Joined: Jun 2024
Posts: 4
Likes: 0
e350
Thanx for all of the support guys. So I did have the conductor board sent out for repairs for speed sensor codes. The conductor plate fixed the 0718, 0719 y3/8n1 codes. What is weird while I am scanning the car. The temp fluctuates back and forth from 93*c to -23*c back and forth back and forth. The converter code was not present before the conductor board repair.
Super Member
Joined: Dec 2018
Posts: 857
Likes: 501
From: Washington, DC
2007 S600, 2007 Chrysler 300 SRT8, 2000 C5 Corvette, 2017 Mustang GT, 2023 300C, and a 2019 Lincoln
I may be wrong but it sure sounds like you are a little low on fluid. After it warms up, the fluid level is slightly higher and your problems disappear. I am guessing you are a pint shy. I could be wrong.
MBWorld Fanatic!
Joined: Aug 2014
Posts: 5,322
Likes: 1,678
S500
outside the appallingly bad gearbox - the torque converter lock up clutch is a failure waiting to happen as these cars age - it cuts in and out all the time as the car is driven
in the early days, it only came on like overdrive in 3 and 4 (on old GM 4 speed autos from 1990's) and dropped out with moderate acceleration to protect it... but as they got more confidant (AKA more evil wanting to steal our money) its on in all gears nearly all the time dropping in an out like crazy - ready to help it fail
seems the early ones had a weaker 2 plate set up than the 2008 mini facelift ones that got 3 plate torque converters
in the early days, it only came on like overdrive in 3 and 4 (on old GM 4 speed autos from 1990's) and dropped out with moderate acceleration to protect it... but as they got more confidant (AKA more evil wanting to steal our money) its on in all gears nearly all the time dropping in an out like crazy - ready to help it fail
seems the early ones had a weaker 2 plate set up than the 2008 mini facelift ones that got 3 plate torque converters
