the tcc is in the transmission and can be accessed by removing the pan on it ,but that wont stop it from shifting gears,its in limp mode and needs to be scanned to find out for sure whats causing this to happen,a bad speed sensor will cause this too happen or a bad tcm unit,don't let no one mess with it that doesn't know what their doing though they can create more problems than you can repair,it normally cost about 300bucks to replace a bad tcc solenoid,but hae shop check it that knows what to look for,good luck.