Vehicle applicability: This diagnostic supplement covers multiple Ford vehicles and engines. Follow the application named in the source below. Some references apply to vehicles other than Mustang.
1-128 Description and Operation
Thermostat Monitor
Thermostat Monitor
Overview
The thermostat monitors identify a thermostat concern.
Thermostat Monitor
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.
Heavy Duty Thermostat Monitor
During a cold start, when the thermostat should be closed, the heavy duty 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 during a cold start. After passing the cold start monitor conditions the actual engine coolant temperature is continuously compared to the thermostat regulating temperature threshold. If measured engine coolant temperature drops below the thermostat regulating temperature threshold the cold start monitor is enabled again and the timer resets. If the engine coolant temperature is too low, the thermostat may be stuck open and a DTC sets.
2016 Powertrain Control/Emissions Diagnosis, Gasoline Engines, 3/2015
2016 Mustang workshop publication supplied to Mustang Atlas. Original technical text and illustrations; HTML formatting by Mustang Atlas. Source page numbering is retained for traceability. Follow the configuration, revision, warnings, and cross-references in the material. About this edition.