Sounds like the PTCM or the FCM got caught in a weird "state of mind". I'm wondering why, but who knows - anything with a microprocessor can 'get into a bad loop'.

This is how the fan works:

The PTCM sends very short pulses to the FCM periodically. The FCM responds with pulses - so long as both modules see the pulses from the other, all is well. If the PTCM wants the fan to run, it makes it's pulses longer, but the FCM responds just the same, - with a pulse in reply to each one sent to it by the PTCM.

Now, let's say the wire between the modules goes open, is cut, or what ever. The FCM won't see the pulses and will 'know' that it has no instructions on how fast to run. So, it goes into EMERGENCY MODE. It runs the fan at full speed at all times to protect the engine. At the same time, the PTCM won't see pulses from the FCM, so it lights the little radiator light, indicating that it senses a failure with the cooling system (the failure is that it can't communicate with the FCM).

If your CHECK ENGINE light came on and NOT the Radiator light, that would be an indication that the PTCM was off in looney-land, not sending pulses to the FCM and (probably) not doing other stuff as well. Yes, you did reset it, kinda like rebooting your PC.