My 2012 Prius sometimes shows a high (coolant) temperature warning light. Symptoms: 1) always after cold start 2) Cabin heating stays cold (really cold) 3) Radiator stays cold (fan runs (observed 1 time) 4) After stopping engine (car fully off and on again (reboot), cabin heating starts working again. 5) No coolant leakage 6) No OBD error codes It happened the first time at the end of my warranty period, dealer checked it, had the coolant system pressurised and couldn't find anything. This is not happening all the time, but time between events decreases. Where to start diagnosing or fixing before my engine crashes.
It could be that the engine water pump is going bad. To diagnose, use a scanner to monitor the engine coolant temperature.
You don't have your miles, but kinda sounds like you are might have a sticking thermostat, or failing coolant pump, or both. Do you have any scan tools to check if the coolant pump is functioning correctly? That would be the place to start.
Yes, no error codes could be found with ODB2 reader (carscanner). WIll hookup my Techstream to search deeper. Cooing temperatures are fine when everything works well. When I had issues (no cabin heating), the cooling water temp fluctuated beteen 40 adn 60 degC. After restart it was ~90 deg C.
