hi, been using search but i havnt come across this exact problem, so i am hoping that someone could steer me towards the right thread...

just got home from afghanistan and a buddy is trying to sell me his merc. 2001 c240. it has been sitting for a year, and right before we deployed he accidently drained most of the A/T fluid while attempting an oil change(you dont have to say it, i know :O ).

he drives down the street to get it flushed and filled, and says afterwords, it started shifting hard. he calls the dealer, which sells him a small electronic part that he installs in the pan, starts the car up, and it no longer goes into any gear but park.

so, does anyone have any idea what would cause the hard shifts?(i am used to the vacuum module on my diesel, but i am guessing the gassers dont have those)

and can anyone wager a guess as to what the part was, and how he screwed up the install? it has been a year since he installed it, and cant remember what it was.

i am a competant wrench monkey, but usually stay away from anything more in depth than a torque converter on A/T's. any help would be greatly appreciated. thanks

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91 300D, 194,000m
08 Tacoma prerunner
92 Nighthawk cb750
65 Mustang coupe 67,000 original miles
05 murry lawnmower, ellz yeah
01 c240