Thermostat Monitor
WARNING: This page does not describe the selected car, but rather 27 other vehicles, including the 2021 Lincoln Navigator, 2021 Lincoln Nautilus, 2021 Lincoln Corsair, 2021 Lincoln Aviator, and 2021 Ford Transit-350 HD. However, it is still accessible from the selected car via links, so may be relevant.
During a cold start, when the thermostat should be closed, the thermostat monitor uses intake air temperature, engine speed, and engine load to predict the engine coolant temperature. Once the predicted temperature has exceeded a target temperature for a length of time, the actual engine coolant temperature is compared to its required threshold. This threshold is 11°C (20°F) below the thermostat regulating temperature. If the engine coolant temperature exceeds this threshold, the thermostat is functioning correctly. If the engine coolant temperature is too low, the thermostat may be stuck open and a DTC sets. This monitor is executed once per drive cycle during a cold start and has a run duration of 300 seconds.