I was looking online for possible causes to this issue on my 06 Cooper S Automatic and possibly a good recommendation on what to look into. I can tell you for one I WILL NOT BE TAKING IT TO THE DEALER soo please spare the "take it to dealer" comments lol. Below are the details:

Model: 2006 Cooper S Checkmate Edition
Transmission: Aisin 6 Spd Auto (NON CVT) GAF21WA-TANA
Mileage: 123k

Trans keeps getting stuck on 3rd unless I shut car off and turn on again. If I drive it on highway it will go thru all 6 gears fine but when I slow down to speeds under 3rd gear, it gets stuck there and from a stand still, it will take time to gain speed (almost like when a clutch is bad on a manual car) and will not down/up shift until shut it off and turn on again.

I have been trying to get this fixed for over a year now to NO avail and need it fixed! I want to just go with replacing the trans BUT have read this trans GAF21WA-TANA is a 1 year, 1 model only trans and I have yet to find one!!! I have been looking for one for almost 2 years now but mkost are manual, older/newer or non S models. I am stumped and want to hear from you all who appear to be the professionals. All the shops I have taken it to want to always quote trans replacement at thousands of $'s.

Any help or direction to help this baby would be GREATLY appreciated!!!!

 

Sounds like the shift solenoid may be sticking.