either the cooling fan relay is stuck on or there is a short in the wiring going to the fan. there is no way the temp sending unit or sensor can cause the fan to stay on. All the temp sensor/sending unit does it tell the engine computer what the engine temp is/tell the gauge where to indicate.
Find the cooling fan relay and disconnect it. If the fan stays on, there is a short in the wiring going to the fan. Most likely it will be a short to ground, possibly a wire rubbed through on a bracket or burned and melted on the exhaust.
