Enhanced Thermostat Monitor

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The enhanced thermostat monitor helps to reduce the time it takes to identify a thermostat concern. This monitor is executed once per drive cycle during a cold start and has a run duration of 300 seconds.

During a cold start, when the thermostat should be closed, the enhanced 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 DTC P0128 sets.