Thermostat Monitoring

Thermostat Monitoring

System Schematic





Description

This monitor operates once per drive cycle. It calculates the difference between the measured coolant temperature and an estimated temperature that is derived from a model. When the estimated temperature reaches a calibrated threshold then the error between the two temperatures is accumulated. The model used to calculate the estimated coolant temperature has look-up tables that use a number of engine and vehicle parameters (engine speed, engine airflow, vehicle speed and the difference between intake air and coolant temperature) to derive compensation values. These are added or subtracted from the estimated coolant temperature as appropriate.

An after start counter is also included. The estimated coolant temperature is taken as the measured coolant temperature for a calibratable time following engine start (this time is dependant on the starting coolant temperature) to overcome second order effects which introduce inaccuracy into the estimate of coolant temperature.

A normal judgement is made if the measured coolant temperature reaches 80 degree C and the accumulated error is not above the failure threshold. A failure judgement is made if the accumulated error equals or exceeds a calibratable fault threshold before the measured coolant temperature reaches 80 degree C.