Therefore, there isn't a single "location" you can point to. To reach them, a mechanic would have to:
1. Drain the transmission fluid.
2. Remove the transmission from the vehicle.
3. Disassemble the valve body (within the transmission). The solenoids are inside the valve body.
If you're experiencing transmission problems, it's best to take your Grand Caravan to a qualified mechanic or transmission specialist. Trying to access and replace these solenoids yourself without the proper knowledge and tools is very difficult and could potentially cause further damage.