LAC SKY/ JohnWR - First, thanks for the taking the time to read and respond. in order:
occasionally, it will heat to 217º-222º but then immediately the fan kicks on a shoot down to 199º. I would say 85% of the time, it's consistently 199º-201º
no puddles or fluids under the car at the moment. The expansion tank is at operating level. I do hear the fan running while I drive the car. It does run when I turn off the car and pump gas.
This sounds perfectly normal to me.
I have not tried resetting the battery. I can do that tonight. I have the GMPP stage 2 on my car, so I always hate disconnecting the battery then the CPU has to re-learn the tables for my stage 2. (takes about 500 miles for a full re-learn)
I am a former GM employee. I bought the car brand new. It is the original coolant fluid. My initial thought of the failure was some kind of physical damage cause by the unbanding of the belt turning and hitting a wire. But...I inspected it well down there and could not any evidence of damage.
I do not see any need to "reset" the ECM. That doesn't mean that it won't help, but this code is not learned, as far as I can tell, so resetting it as you have done is all that should be necessary.
I determined it was the FCM but deduction. I learned the FCM is a relay by reading on the forum and websites. Relays tell the fan to turn off and on. When I determined there are no Relays in the fuse box for the 2.0L, the only other RELAY option was the FCM, so I replaced it because it was plug and play.
Technically speaking the FCM is not a relay, it is a variable speed controller. Relays turn on and off, a speed controller modulates. The 2.4 has a relay module that provides high/low/off fan speeds, but the FCM gives the 2.0 infinitely variable fan speed.
This code is purely electrical, so as long as the car is operating at normal temperatures there is no reason to worry about coolant, bubbles, thermostat, water pump, etc. When you have it reset does it come back before the fan comes on, or while it is running?
Possible causes of this code are the ECM, the FCM, the fan, and the wiring or connectors. Because it happened only after the belt broke up I am still suspecting some physical damage to something. Check all of the connectors by unplugging them and plugging them back in, and look at anything that could have been hit by belt debris.