The coolant tank is a surge tank.......since you indicate it had a bit of coolant remaining, the engine was never actually low.....just the tank.
Odds are nothing is harmed.......but keep checking it to see if the level stabilizes.....add as required.
I suspect, though, there is some air in the system......that would line up with poor heat and the fans going to high speed.
The service engine light may be related to the coolant temp sensor (for the fan control).
It seems the coolant temp gauge will only show hot when the engine is actually overheating.
Keep in touch,
Rob
Odds are nothing is harmed.......but keep checking it to see if the level stabilizes.....add as required.
I suspect, though, there is some air in the system......that would line up with poor heat and the fans going to high speed.
The service engine light may be related to the coolant temp sensor (for the fan control).
It seems the coolant temp gauge will only show hot when the engine is actually overheating.
Keep in touch,
Rob