Overheat message, no CEL error code

So you are proving out the circuity from the DME to the fan and that the fan works. Also, you previously replaced the sensors and the only thing left is the DME. So if it were me, I would replace it. Clearly if you got a faulty temperature sensor out of the box that would throw a wrench in this but that is highly unlikely that you would have an issue and get another sensor that causes the exact same issue.

The manual does not state specifically what is done when you program the DME. It does need to be programmed but without the detail about what is done during the programming I can't answer that.

As you can see from the attachment the immobilizer system is part of the programming but this is normally just a back up of the information and does not require to be done in order to start the vehicle.

So to answer this question, I think you will need to call a dealer and ask one of the technicians this question. I have not replaced one of these with a used unit so I don't know for sure.

Sorry I can't answer that but I don't want to tell you that it can be used and then be wrong. Nor do I want to be on the safe side and say it can't be used and you spend more money then you need to.

Sounds great. Let us know if you do. That is good info that will help others in the future not to mention me as well.

Normally yes, but that is when the entire unit fails or something that effects other circuits like a 5 volt reference circuit. Unfortunately with this issue it is a single circuit on the board within the DME that is most likely open. This means it is a single contact that is used to send voltage to the fan and the DME is not doing it. Clearly the fan can work as you can command it on but the circuit within the DME that is supposed to do this is not. So if there were other things on this same circuit in the DME then it would not work either but unfortunately there is not, it is just the fan. There are no codes because there is no feedback signal from the fan that is telling the DME that it did not actually turn on. The signal that it is not working is the fact that the fan does not work. With no feedback circuit, the DME just turns the fan on and it has no clue if it does it or not. It only knows the temperature is too high so it displays the message on the cluster. It would be nice if it displayed "Overheat due to the fan not coming on and the DME is the issue" but it doesn't so we have to piece it together like this.