I have a 01 automatic honda civic and what's happening is when the car heats up after 20-30 minutes of driving the transmission will go into fourth gear and not come out unless I manually put it in D2 or D3. If I turn the car on and off its fine until I come to a stop then it gets stuck in fourth again. My D light is burnt out so I can't see if it's flashing but I'm thinking it has something to do with my Transmission control module. (TCM)

My question is, where is the TCM on the car and is it the same computer as the ECM (Engine Control Module)?