Here's a list of possible problems:
*You may be actually overheating. Check plastic cooling parts. Check coolant level. Bleed system.
* You maybe have a bad actuator stuck in the open position.
* you may have a problem with the wiring to/from the PCM
* A bad PCM (Least Likely). The actuator looks for a pulsed ground from the PCM that sets the fan speed.
Your best bets is to do a thorough bleed the system, replace thermostat and broken plastic cooling parts, and refill with coolant.. If same results, proceed.
Now saying that, check your fan fluid as it should be RED. If it's any other color such as pink (common) or brown, etc... change out the fluid. Disconnect the return line from the fan pump and spin the fan until fluid comes out the hose, drain into a basin and dispose accordingly. Reconnect the return line, fill back with the proper ATF (I forgot the exact kind, but other members should chime in here with the right one) and run a can of seafoam in there. Now granted that the seafoam does do the trick of getting the actuator unstuck, drain out the fluid one more time and refill with new fluid without seafoam. (I do not speak for seafoam products. Other users have reported great success with them and I am passing the info along to you; do this at your own discretion) If same results, proceed.
As far as wiring goes you can disconnect the fan actuator via the wiring harness, and see if the fan returns to low speed. If it does, there may be a problem with the wiring from/to the pcm or a problem with the PCM. Note that the fan will NEVER stop spinning as long as the engine is running. If same results, off to the dealership.