None of this makes sense. The engine cooling fan (we ARE talking about the engine fan, right?) system is very simple. The ECM tells the Fan Module how fast to run the fan. It starts the fan up at about 180F water temp, by the time you get to around 210F, the fan is running at 70-80% speed.

If you turn the A/C on, the fan will run at about 120 rpm unless the engine is getting warm, then it will speed up as described above.

If the fan module and ECM can't communicate, two things happen:
1) The ECM lights the "low coolant" light to indicate that you should go to a dealer with a blank check, a jar of vasoline and a receptive attitude to spending money.
2) The Fan module enters "emergency mode" and spins the fan at 100% warp drive speed to protect the engine.



Ya got me on this one.