By chance, did you get a diagnostic trouble code retrieved? If so, can you let me know what you found?
In general, the error you identified seems to be related to the engine coolant thermostat. Older vehicles used a mechanical type thermostat, but on newer vehicles, an electronic thermostat is used.
Although the electronic thermostat does the same thing, it is controlled by the powertrain control module (PCM). The PCM receives a signal (based on coolant temp) and adjusts the thermostat position accordingly.
When the thermostat signal doesn't change or isn't what is expected for an extended period of time, the PCM will set a heater thermostat control circuit code. Please understand, this is my theory right now without having a diagnostic trouble code. If you haven't already, have it scanned to see what is stored. Most parts stores will do it free of charge.
To take it one step further, if you are getting an "open" indication, that indicated either the sensor has failed or there is a broken/disconnected wire not allowing power to pass.
Let me know if this helps. I'm sorry I couldn't be more specific, but if you do have it scanned, let me know what code is found and I can better assist.
Sunday, January 29th, 2023 AT 1:46 PM