2006 MCS 6 speed auto shifting erratically
 

Help... I am a pretty good back yard mechanic (been building and working on cars for 35 years) and I can't figure this one out. My daughter has a very nice 2006 MCS with the Aisin 6 speed automatic transmission. The car currently has 81K miles on it. She bought it about 2 years ago with 60Kish miles. I ran and drove great for 6 months or so. One day on the freeway it just randomly shifted into 1st or 2nd gear all on it's own. No warning, no reason, speed was steady and the transmission was in D. She never drives it in SD or manually shifts it. This has been going on ever since for the last year and a half. We have replaced the transmission with a warrantied used unit from a rear end wrecked car with less miles than the original about 8-9 months ago and replaced the fluid at that time. We have had the ecu reset. We have looked at codes and it was saying speed sensor faults so we replaced the speed sensors on all four wheels. The problem still persists. I drove it last night after she drove it over to my house so it was already warm and it works perfectly for the first 2 miles or so. That's when the shifting issue starts. It shifts down very abruptly first then it acts like it can't decide which gear to be in. It jumps all through the range up and down. The ABS light and the DCS lights turn on. Sometimes when you come to a stop at a light and try to start moving again the transmission is in a super high gear and the car will barely move. You have to work the throttle until it shifts down and will start moving. I brought it back home and reset the ECU and took it out for another drive on the same exact route. No lights were on and it drove great until almost the same exact point and it repeated everything. I'm at a complete loss and ready to throw in the towel. The dealer just says "new transmission" but I know it can't be that and we aren't spending another $8K on this thing. I know it has to be some sensor somewhere and something "telling" the transmission bad information. Could it be the ECU has gone bad? I've read they are very difficult and costly to replace. I have searched and searched online and through forums and I see similar issues but no one seems to have a solution that fixed it. If anyone has more ideas please let me know. I can perform most mechanical duties and some electronic ones before just taking it to the dealer... again.

Really? 52 views and nothing??? Anyone know another forum to post on for user feed back?

Well Im getting ready to buy a 2005 s auto that is having the exact same problem. we cant be the only 2 to have this problem. this car too has been hit in the rear and the owner said thats when the problem started. I'm hoping you have found a solution. any ideas?

OK, now you guys are scaring me. I just bought a 2011 countryman with paddle shifters. I also own a 2005 BMW Z4 with paddle shifter. I call it a sluge-o-matic, because sometimes it just kind of sluges into gear. I don't have a solution to your problem. But, maybe someone on the BMW forms might. They might be different transmissions, but they were both engineered by BMW and could share similar problems.
Good luck

this sounds like an electrical problem to me.....so i would think that a 'new transmission' would be a waste of money. do you live in a metro area where there might be indy shops that specialize in electrical issues ?

My BMW Z4 as stated previously, shifts much better after I had the "Life time" automatic transmission fluid changed. Not cheap on a mini. I, being new to mini's inadvertently drained the transmission fluid instead of the oil. The trans fluid looked black, and it's only 6 yrs old. $35/quart x 5 qts + $248 to install it. Still cheaper than a new transmission. I don't believe in Life time fluids and would have changed this shortly anyway. So, no big deal.