Creepingdeath94

Alright, sorry in advance for the novel here but I wamted to be thorough up front to answer as many questions to get to the heart of the issue here.

1st off, its a 2003 c240 base sedan, 187k miles. Not sure that the trans fluid ever was changed as it was pretty dirty looking but not burnt smelling or anything. I have done quite a bit of searching and havent seen anything quite like mine is doing. My understanding is these transmissions are pretty solid as long as they arent totally neglected to the point of failure or have the valeo radiator failure (doubtfully ever the case here or long resolved given mileage and age now).

Anyway, this car was picked up recently in trade and had a trans issue where it would drive and move normal until warmed up some then drop to like a neutral even though in drive or reverse and just rev...like slipping trans. I did the conductor plate, 13 pin connector, filter and 4 qts new fluid and it drove fine for almost 30 miles before doing it again now.

My question here is how sensitive are the trans electronics to dirty/particles in fluid? Can a solenoid or something on the board be not allowing pressure somewhere making it seem like neutral? Do any of the solenoids typically fail causeing a neutral like issue and not the typical limp home mode? The orings on the solenoids were good when I did the conductor plate swap. Am I going to need the mercedes specific code reader to get TCM codes or are there typically 1 or 2 places that cause this? Or is there an off chance I got a bad conductor plate or it didnt like not haiving all new fluid replacement when I replaced it? I find it hard to believe its in the transmission and not electronics due to how well it drives and shifts cold, and even warmed up to operating temp for the 30 miles before it started acting up again. Just want a direction to go without having to just shotgun parts but if I have to get a mercedes shop to read out the TCM to really get this resolved, then I guess I have to go that route. I just dont want to spend $150+ on a scanner Ill use a couple times and likely never need again. Especially working in a shop with specialty tools right there that cant read the car I have.

Thanks all and I do appologize if this is covered somewhere but I have google searched and looked through this forum and all the trans related issues are the typical limp home and shifter stuck typical ones and mine is just a bit different. Just dont want to condemn the transmission assembly if its not the real issue and it just gut feeling seems like its electronic.

Creepingdeath94

I also wanted to ask a follow up/diag question. If I unplug the 13 pin connector at the trans, it will drive but in a limp mode correct? Or will it not start if I do that as the conductor plate has a starter cut off on these cars correct? Basically, would putting it in a limp mode at least let me see anything like if the issue still happens and neutral/slip issue occurs after warming up a bit or if in limp mode it carries on driving longer. Just spitballing without a proper code reader at the moment.

krazzdav

did you check the trans fluid level with dipstick at 80c? from what i understand you dont want it high or low or will cause issues
maybe the fluid was low/high when you purchased it? less than 4 qts is about what you need just for a filter change
if you overfilled you will need to siphon fluid out (a little add/removed makes a big difference on the dipstick)
if the fluid level is fine you will need to scan the TCM/ECM for faults (I have MB Star myself and not sure what other scanners are as good)

no the car wont drive with TCM unplugged but will start from what i understand

perhaps someone else can chime in about specific conductor plate and solenoid symptoms

Creepingdeath94

The level acted weird on occasion with it reading high while running like checking not running when issue occured initially. I checked level and had it were it should be after doing conductor plate work but need to check again now. If it is reading high again while running I think I will be suspecting bad or failing trans pump as there is a whine sometimes when it initially starts doing this no drive issue but goes away after a bit more running...but sounds like when a pump is starving for oil even when I know it has enough.

Creepingdeath94

I am going to check fluid level again tonight when I get off work. Doing some more digging here, is it possible the shifter mechanism can cause weird issues like this? I know they have inherent problems too but I thought that was more of gear selector will not go out of park and odd shifts and not so much slipping and driveability issues. I checked the TCM and it did not appear to have any fluid as if it had wicked up the wiring andngotten into it, but do the TCM or shifter electronics affect fluid path internally in the trans to give pressure issues or tell pump/torque converter to do anything that could cause this? I just dont see how a trans pump can fail pretty much instantly as its such a simple design usually and the whine noise is not all the time. It seems odd to be something mechanical would come and go like this and that electronics somewhere are the culprit, but like I said in my main post, I am not a mercedes tech. Thanks again.

krazzdav

the fluid must also be at proper temperature and can't check like a typical car "while running"
it should be to the top of the dipstick when cold prior to starting for a rough idea then have to heat it up by driving to 80c