Diagnosis of Thermostat

Diagnosis Of Thermostat

Due to a missing or stuck open thermostat the cooling temperature rise is delayed, especially at low ambient temperatures. The picture below shows an overview of the monitor. The thermostat monitor is designed to detect a delay in the warming up of the engine coolant temperature. Therefor the calculated reference temperature (based on coolant temperature at maximum heat radiation with functioning thermostat) is reused. At enabled monitoring conditions the difference between the calculated reference temperature and the coolant temperature is checked. If the difference is above a calibrated threshold for a calibrated period of time and the calculated reference temperature has not yet reached its maximum value, the fault is detected and its fault code is set. If the difference remains below the calibrated threshold for a time period longer than the above mentioned time an error from a previous warm up cycle may be cleared as soon as the calculated reference temperature has reached its maximum value.







Monitoring conditions:
- Monitoring conditions for engine coolant temperature sensor plausibility check (warming up check) must be fulfilled
- coolant temperature at engine start in between two thresholds.

Additional conditions for clearing purpose:
- integrated air mass flow > calibration
- engine start temperature near the start temperature of the trip when the faulty thermostat has been detected.

Diagnosis of Thermostat