w210 owners - clean those TCMs!!!
 

I've read about the w210 problem of transmission fluid migration from a leaking connector on the transmission, up the wiring harness and into the transmission computer. I replaced the round connector at the transmission a while ago as it was weeping slightly, but never looked inside the TCM. Really, I had no reason to - no codes, no transmission limp mode, no shifting behavior that I would call offensive. That said, I always thought the up-shifting happened a little too soon, so that the car was in a higher gear than necessary. I also thought the shifting felt a little tired. Not sure how else to describe it. Again, nothing particularly offensive, just that it wasn't as quick and responsive as I would have liked.

So yesterday I decided to pop open the TCM out of curiosity, just to see if any fluid had wicked up into there. Sure enough, the circuit board was wet and there was a few ounces of reddish brown fluid in the bottom of the plastic casing. I used a spray can of electronics cleaner, and cleaned the board, the casing, and the harness connectors really well. Then let it all air-dry in the sun for an hour or so before re-assembling.

Been driving around all morning today, and holy moly this car is now a rocketship! You push the go-pedal and the rush of torque pushes you back in your seat, passing all other cars on the road effortlessly! No more sluggish shifting, no more waiting for the transmission to downshift anytime you want to pass someone. A simple cleaning of the TCM has changed the entire character of the car. It feels so snappy and responsive now.

Moral of the story - if you own a w210, open up and clean that TCM. Even if you have no obvious problems, you may well have fluid in there negatively affecting the shifting and drivability of the car.

I know this is old but I did this today. Well the opening up part to see if TCM was wet. It was dry. Like my trans pan! I had to add 2 qts to get it to show on dipstick. I have zero leaks. Dunno where it go

Is this a difficult and messy job? I'd think if it were simple then everyone would be doing it and there would be no need for these posts. I've seen the plug that needs replaced to havea good seal, but have no idea where the TCM is.

The TCM is in the control unit housing on the passenger side of the engine room.

Interesting, hopefully this helps me.

But I don't know where it is, the description above is very vague.

Location:

https://www.google.com/search?safe=strict&source=hp&ei=7c1mXczqOovL0PEP__KfgAI&q=w210+tcm+location&oq=w210+tcm&gs_l=psy-ab.3.1.0l2j0i22i30l2.1375.4683..6916...0.0..1.350.1701.4j3j3j1......0....1..gws-wiz.....6..0i131j0i308i154i357j0i10.QjF99RIQGXE

I'm replacing my engine air filter tonight, so I'll open this area (for the first time!) and have a look. Excited to get out of work and get home now.

your W210 has a black box on the passenger side in the engine room, it holds the ECM, TCM, ABS etc - once you unscrew the cover off.