Thermostat monitoring system and method

Abstract

A thermostat monitoring method includes measuring an engine coolant temperature with an engine coolant temperature sensor a predetermined amount of time after engine startup, determining with a controller one of four zones to determine whether a thermostat will pass or fail, based on the one of four zones determined, accumulate with the controller one a pass index or a failing index, when the pass index reaches a first threshold, reporting a pass with the controller, and when the failing index reaches a second threshold, reporting a fail with the controller.

What is claimed is: 
     
         1 . A thermostat monitoring method, comprising:
 measuring an engine coolant temperature with an engine coolant temperature sensor a predetermined amount of time after engine startup;   determining with a controller one of four zones to determine whether a thermostat will pass or fail;   based on the one of four zones determined, accumulate with the controller one a pass index or a failing index;   when the pass index reaches a first threshold, reporting a pass with the controller; and   when the failing index reaches a second threshold, reporting a fail with the controller.   
     
     
         2 . The method of  claim 1 , further comprising
 comparing the measure engine coolant temperature with an estimated engine coolant temperature.   
     
     
         3 . The method of  claim 3 , further comprising
 comparing the engine speed with a threshold engine speed.   
     
     
         4 . The method of  claim 3 , further comprising
 comparing the engine load with a threshold engine load.   
     
     
         5 . The method of  claim 1 , further comprising
 determining with the controller whether the thermostat has failed previously.   
     
     
         6 . The method of  claim 1 , wherein
 when the controller has determined that the thermostat has failed previously the passing index is increased by a first increment.   
     
     
         7 . The method of  claim 6 , wherein
 when the controller has determined that the thermostat has not failed previously the passing index is increased by a second increment, the second increment being different from the first increment.   
     
     
         8 . The method of  claim 1 , further comprising
 resetting a pass/fail counter.   
     
     
         9 . The method of  claim 1 , further comprising
 incrementing the failing index only when a predetermined model is greater than or equal to the engine coolant temperature.   
     
     
         10 . The method of  claim 1 , further comprising
 incrementing the failing index by a predetermined amount when the engine coolant temperature is less than a predetermined temperature.   
     
     
         11 . The method of  claim 1 , further comprising
 incrementing the passing index by a predetermined number when the engine coolant temperature is greater than a predetermine model and the failing index is 0.   
     
     
         12 . The method of  claim 1 , further comprising
 varying the failing index can vary based on engine load.   
     
     
         13 . The method of  claim 1 , further comprising
 incrementing the failing index by a predetermined number when the engine coolant temperature is less than a predetermined model and the predetermined model is less than a predetermined temperature.   
     
     
         14 . The method of  claim 1 , further comprising
 decreasing the failing index by a predetermined number when the engine coolant temperature is greater than a predetermined model when the failing index is greater than zero.