So im in a rut, I just purchased a high mile 241k 2003 ML350 inspiration package for 300 bucks. Total steal, needed a jumpstart to turn over and it has a tranny problem. I have had a few cars with the 722.6 and done work on them in the past. Essentially when I first got the car it would go into gear and move literally only half an inch (forwards or backwards) and the transmission would slip, car would rev and it would cut power and ultimately go now where. So I trailered it home and got to diagnosing. The guy who sold it to me said it was driving fine, had been shifting great then cut out in a parking lot and dropped into neutral and had to be pushed into the spot. Hasn't moved since. But previously no hard shifting, no leaking fluids, and no transmission slippage. I know these trannys are usually pretty strong and reliable, but with frequent electrical issues. Read the tranny codes with my icarsoft scanner which showed
P2600- Voltage to circuit 87 has under voltage
P2401- left rear wheel run signal sent from traction system Via CAN bus implausible
P2315- one or more messages from control unit A1 not available
P2502- The gear is implausible or transmission is slipping
P2601- Voltage supply of circuit 87 has over voltage '
So to have the electrical business covered I ordered a new conductor plate, gasket, filter, and electrical connector with fresh O rings. I dropped the pan, found dirty oil, no metal shavings, and the film in the bottom of the pan wasn't bad. A little was present of just grime but for 241k it looked normal. Conductor plate when in without problem, this was my third one I have done on different 722.6's. So The big find was the electrical connector was SOAKED in fluid. Leaking outside the transmission, and all along the bottom of the car. Not much output but definitely had been leaking for a while. I hoped this to be my BIG find for electrical problems
. Put in a new connector made sure the 7mm screw was nice a snug, and I cleaned the connector really good with electrical cleaner, WD40 and dried it. Plugged it in, added fluid, and bingo car drives! I was able to drive it in my driveway, it moved about 25 feet and then made a little thud and fell out of gear. Car stayed in drive, slight whiring sound, and would rev without any power cutting and would move nowhere- This is new. Same for reverse, whir, rev, and no movement not even the 1/2 inch from before. It would spin the transmission insides and when placed from D or R to park real fast it would make the parking cog click click click unit it stoped. Ran the codes again and got only a code for transmission gear implausible, transmission slipping, and it wouldn't let me clear the code. No limp mode or lights on on the dash. Tried the tried and true on and off with the ignition and no change. I jacked the car up unplugged the connector which was still a little oily from the first leak and plugged it back in.... Bingo the car drove again! Drove it down the street shifted smooth all the way to 5th and came to a stop backed up to turn around, put it in D, it moved 10 feet then popped out of gear again. Same still showing D, whiring, reving up when hitting the accelerator, no lights, and not going any where. Dammit.. So I unplugged it plugged it back in and it didn't work
. So I had a friend tow me the 1/8th of a mile back. Did a lot of research online through all the 722.6 forums and still not too much luck. I think it must be electrical as it can be fixed and works fine at times, but then fails. I imagine a mechanical failure would never allow it to work properly.
I looked at the connector plug, cleaned it again and read that fluid can wick up to the TCU. Well I followed the wires up, made it to the TCU by the accelerator pedal and sure as shit isn't it a little oily
. Unplugged it, cleaned both connectors medium well, took the TCU apart which only had a drop or too at the connector pin, zero inside on the chip. The two harness plugs were very oily for the TCU, cleaned that medium well with electrical parts cleaner, dried it. Plugged every thing in (including unplugging and replugging the connector on the actual tranny) and bingo it works! Drove it for 5 miles, drove like a champ, smooth shifts stop and go, backwards, and I just took it easy on it. Well driving home I gave it some goose and it popped right out of gear after a hard pull, dropped out at like 2500 rpm, never really got it wound out. Needless to say I towed it home again, with a friend and a chain
. So I am like WTF works then doesn't. I unplugged the TCU by the gas pedal, turned it on and it whirs like when it dropped out of gear, allows me to shift from PRND and nothing happens movement wise. Plugged the TCU back in, nothing. Unplug the connector on the tranny and put it in and it resets. Weird that it resets on the downstream but no change when unpaged upstream. This makes me believe my wiring from the TCU to the tranny connector is bad at the lower connector spot...? I do need to check the transmission ground. It looks okay but hard to reach.
Does anyone have any input or suggestions to try next. I feel like I covered the bases and have a suspicion for bad cable from the tranny fluid leak. What scares me is that it dropped out of gear under some higher load, Im assuming that has nothing to do with the electrical draw/demand for the transmission. Also light brake switch has not been replaced, brake lights do work. And the last few times it has popped out of gear putting it in park does not engage park- it remains in neutral. So despite saying park and feeling the sector go through the motions the car can be pushed in P. But when reset (from unplugging the lower connector and putting it back in- Nintendo style) park reverse neutral and drive all work as they should... Is this a torque converter problem? I can't see a TC failure working again and then stop working then work again? Please help!