andimumxhiu

Hi to everyone.

It has been only 2 weeks since our family welcomed a 2011 E350 blue efficiency . Last weekend i took in on a 1000km trip , and it happened to me twice that the car started to change gears at high rpm (around 2500rpm) and it had a weird smell like a burned plastic. It happened when driving for a long time on uphills. When i came back , took it to a MB licensed service , and they said i had to change the transmission oil and filter. The did it , changed 9 litres of trans. oil and the filter. And today AGAIN ! Same problem , driving in the city. Anyone else experienced the same thing ? What could possibly cause this ? Thanks in advance

beejAMG

whilst changing the tranny oil and filter is a good thing given the age of your car. you sure the car didnt just downshifted when youre goin uphill?

andimumxhiu

It is not a matter of downshift , it stays the same for a longer time. It also wont allow me to use the gear shifters oj the wheel.i am guessing something is causing the transmission to heat up , but was wondering what might be the cause

beejAMG

atm, your guess is a good as mine, i would suggest to take it back to the shop where you had the tranny oil change and have it looked at. work should still be under warranty. have them scan for any faults.

KEY08

If the paddle shifters are inoperative, then you have a problem with the trans that needs fixing. I would not wait on this repair.

T100T

Not sure if this is relevant or not but on my 2010 E550 the transmission will downshift if it detects high temperature. This is because the pump that circulates the transmission fluid through the radiator runs at input shaft (engine speed). So downshifting increases the flow rate through the radiator.

Having the air conditioner on makes this downshift occur earlier.

So, and I'm guessing here, you may have a transmission overheating issue but the shifting may all be working properly.

Peter

Stu1980

Hi All,

Having this same issue with my 2012 E350, Gears changing at around 2500rpm for about 8 miles or 15 min +- whichever comes first. It won't change manually in sport but will change in the manual setting with paddles. The same warm smell from the rear of the car. After this time or distance, it runs normally. Been to Mercedes deals no error codes oils change, mystery.
Did anyone diagnose this issue? Thanks

atraudes

Check out your radiator and see if it's blocked or full of dirt or anything. A restricted radiator could certainly cause overheating issues.

mellonc

Perhaps it's not your transmission which typically show symptoms in other ways like gears slipping. Holding onto gears too long or shifting late typically has to do with not enough torque being generated by the motor - in other words, your transmission is waiting for your engine to generate enough torque before up shifting to preserve forward momentum.

Stu1980

Thanks for your replies, so when I took it to MB they said there were no error codes but it could be conductor plate and pump unit which would cost £1800 but MB couldnt be certain only an educated guess which puts me off as I could spend that money and still have the same problem, the issue is not constant but intermittent which surely if the radiator was blocked it would be constant.
If the gearbox is waiting for the torque to build up would I notice lagging in pulling off and wouldn't error code show up? The car still performs as it should do but ill certainly research that if there any links anyone can send through would be great. Thanks.

Mud

How many miles on the car and any known maintenance that came with it?

Just some thoughts ....
It sounds like a control issue, maybe the TCU (located in the conductor plate) is commanding the shift but one of the solenoids (replaceable, also attached to conductor plate) is not working correctly. And/or debris inside the valve body that's affecting one of the spool valves.

I'm not saying this is the fix but perhaps worth looking into by someone that is familiar with these transmissions. By that I mean someone that repairs and not just reolaces them. The conductor plate can be removed and the valve body halves split/cleaned but needs to be done by a specialist to ensure none of the check ***** are lost and the valve body is correctly checked and reassembled.

Also suggest to clean and check the wiring harness connector at the transmission. Ensures no oil has leaked inside the connector and that corrosion is not a factor.

Stu1980

Hi, Thanks for your reply,

The car has done 118000 miles its had full MB service and Gearbox services done on its intervals. What you are saying there is more or less what MB says to do. So does the TCU control the oil flow and pressure within the gearbox and torque converter or is just for the gear speeds?

Mud

The TCU is the processing/reporting unit for transmission control. It controls solenoid activation which in turn control oil flow through the valve body/spool valves.

I believe from your description that my comments differ slightly in that I left the torque converter alone and also suggested disassembly/cleaning of the valve body. From this distance I'm not convinced that the TCU actually needs replacement, but if they are swapping out the conductor plate it's an opportunity to thoroughly clean the valve body.

Good that the car has a maintenance history - my approach was to start with less expensive things first. That's from a DIY perspective, I realize that you're paying for the work and don't want to duplicate paying for trial and error. But in essence the shop also seems to be in trial and error mode. Star, Vediamo, etc software that accesses deeper operating data should show the transmission operating parameters such as solenoid commands, speed sensor readings, etc. But you mentioned no codes shown, that's why I'm not sure why they want to replace the parts they mentioned. Nothing personal with them, just questioning the proposed work.

Sorry for long post, I'm just trying to think through more minor issues first. With our limited resources at home we sometimes try parts for a fix but I expect a shop to provide an accurate diagnosis before going that route.

Stu1980

Hi, so that why I'm reluctant to proceed with the work because MB said that they think that replacing these part might resolve the issue purely from just years of experience and a hunch any expensive hunch. What would you say the 1st point of call be to start ruling out possible causes? I very much appreciate your post as I'm getting a better understanding of the MB mechanics of the gearbox.

Mud

I'm not discounting the experience of the shop, but I would expect a guarantee of a fix from their recommendation. Otherwise you're just paying to give them something to do on a guess. I also don't know the depth of their analysis - were they looking at more than generic level data for example. A warm smell was mentioned, that could be anything from overheating to an oil leak. Were they able to look at actual operating parameters like controls, pressures and temperatures?

I can't effectively diagnose a cure but as mentioned just presenting my thoughts based on your info.

If you don't know for sure, start with simple. Are connectors ok? Is fluid level correct and filter installed fully into the valve body? Is the valve body itself clean internally and are the solenoid screens clean?

You also noted issue with paddle shifters which is interesting. Selecting E and S changes position of an valve inside the valve body (I think it's called a B valve, can't remember offhand). This in turn changes shift characteristics including durations and starting from first gear for example. Paddle shift is a direct command to the TCU, if not working in one mode (E or S) then I'm back to wondering about controls which again circulates back to connectors, conductor plate and valve body.

If you have ensured VB is clean and transmission is not overheating then a next step may be looking at the conductor plate/solenoids. But that's an internet diagnosis so value here may be meaningless. Maybe OP is still looking at this and has updates from repairs.

Stu1980

Thanks for your reply, what you have said has more sense than anyone or MB mechanic has explained. The only thing is to find a mechanic who understands the logic. Please if you come across any more info please post. Thanks

Doctor Memory

I've heard that the reason the transmission does this is because it gets hot, so it downshifts to increase the pump speed, which circulates the water through the radiator faster. I'd get your radiator checked/flushed and possibly consider getting an external transmission cooler installed.

Mud

Getting an auxillary cooler to compensate for overheating on one of these sedans that doesn't tow anything is a band-aid, need to get to the root cause of the overheating.
Quite often even an aux cooler doesn't solve the overheating, just takes a bit longer to get there.
Overheating that reaches critical level can result in ecm commanding limp-home mode (or shutdown) from what I understand.