CEL P0597

Hey all. I got a CEL with code P0597, "Thermostat Heater Control Circuit / Open". I ran my OBDII scanner for a 10 mile highway drive and found the coolant temp to be ~210 +/- 5 degrees F. That seems optimal so I'm ruling out a mechanical issue, which narrows it to something electrical. I'll have the car on ramps shortly to check connections to the thermostat housing. Where else should I look to potentially solve this? Any leads would be appreciated.