Transmission problems 2004 C320 wagon
 

Just bought one cheap...owner said the transmission was quirky. What research I've done, there seems to be an issue with the transmissions in the C320 4matic. I read they are 'user friendly' meaning they adjust to your driving style over time. It drives fine most of the time but I'm surprised intermittently by Skipping gears and lugging. I also get the 'limp mode'. Is this car a lemon?

The adaptive system goes back to the first 722.6 in 96 so that is nothing new.

You really need to scan for transmission codes , clear them then drive until it acts up and rescan. Doing anything else won't help solve the problem. ( RE changing random parts. )

Hey Clarion,

For starters, got to check the oil level with a testing dipstick, and the oil quality...

722.6 dipstick | eBay

Next, physical thing you may do. Find the TCM(transmission computer) unplug the connectors, and look at them for oil contamination as it super common to see this.. Look at this thread on post 5 if you find oil in the TCM it is the result of failure of the o-rings on the circular connector-post 1.

My attempt at replacing the transmission plug. - Mercedes-Benz Forum

The TCM can be cleaned with contact cleaner. Do about six intervals of spraying, and pat-drying with paper towels, and on the last one pat-dry it, and let the TCM dry overnight standing up...

Do get you codes scanned too..

The fluid you can use is Valvoline Max-Life ATF in the red jug from Walmart...

All the best

Martin

That car is a candidate for the radiator problem that leaks antifreeze into the transmission through the cooler. This almost always causes shuddering on upshifts 1-2 and 2-3 along with other random quirks. If there are no fault codes indicating specific problems like the conductor plate the adaptations are reset and the car is driven. If the trans is better then an updated module is ordered in. If its not better then a glycol test is performed to confirm antifreeze contamination. Worst case scenario is a new radiator and transmission.

Thanks guys. The connector sounds like an easy fix if that's the prob. The radiator/coolant thing...I don't know. I will read the service manual for the trans. The guy I got it from told me he replaced the two Trans Solenoids and that didn't work. I've never worked with codes but guess I will learn. How much do different drivers/driving styles effect the 'smart' trans? Any other experiences with this Transmission will be greatly appreciated.

duxthe1 Wrote:...That car is a candidate for the radiator problem that leaks antifreeze into the transmission through the cooler. If there are no fault codes indicating specific problems like the conductor plate(?) the adaptations are reset(How) and the car is driven(When). If the trans is better then an updated module is ordered in.

New radiator and trans??? How do I check for this? What are and how are 'adaptations' reset? Is this a test for a faulty module? Slightly confused, can you elaborate?

The conductor plate has the speed sensors and connect the solenoids to the harness. When it fails you get limp mode and fault codes.

The adaptations are the learned adjustments to the shift program. Early modules can adapt inappropriately causing shifting problems. If the trans shifts better when the adaptations are zero'd out then there is an updated module that will fix it. Adaptation is cleared using the factory scan tool.

If shifting doesn't improve after resetting the adaptation then there is likely an actual trans problem. Often caused by antifreeze contamination of the ATF from a faulty radiator in early 203 chassis cars like yours. A glycol test can confirm contamination. If positive in any significant concentration then the trans is pretty much shot.

Thanks Duxthe1, and everyone...What are the chances? I live on Kauai and good mechanics, parts, just about anything auto is weak over here, especially for Mercedes. I was talking to a musician friend last night and turns out he worked Merzs for 16yrs. He's repaired many of these transmissions and described exactly what you said. Gonna test for anti-freeze and if clean, an easy fix he said. Thanks for the responses...As the world turns...

According to MBDOC, the evil French radiator was in w203 cars produced from April 2002 to August 2003.

That would include some, but not all w203's marketed as 2004 models. (Mine was built 25 July 2003).

http://www.peachparts.com/shopforum/tech-help/250877-so-when-do-i-pitch-my-valeo-radiator.html

FWIW, I asked the dealer parts guy about this. He says he has never sold a w203 radiator except as collision parts. He showed me the current version, which is also a Valeo, but made in Poland.

Mine is just now hitting 100K miles, so I think I will go ahead and get it changed, just for feel good.

I sent in a transmission oil sample to Blackstone about 2 years ago, and it had no water or glycol at that time.

The bulletins do say that but I have seen as late as 2005 model year 203's with glycol contamination. Its also not a problem exclusive to the 203 chassis. In fact we wont sell a used 722.6 without a glycol test first.

Since the conversation is on Glycol test, whose kit do you recommend?

Thanks,

Martin

We use gly-tek from Nelco. they come 10 tests per kit

Good to know, thanks. Confirms my suspicion that I ought to get mine changed.

Just curious, are you located in the rust belt?

Not in the rust belt, its a high desert here. A little salt is spread in the winter but the humidity is nonexistent most of the year.