Theory Of Operation

The purpose of this diagnostic is to verify that the engine coolant temperature has reached a certain value (pass temperature) within a calibrated amount of engine run time. Engine run time is based on the start-up coolant temperature; the lower the start-up temperature, the more time allowed for the Engine Coolant Temperature (ECT) Sensor value to reach the pass temperature. If the engine coolant temperature does not reach the calibrated pass temperature before the engine run time reaches the maximum time allowed for this diagnostic, a failure will occur.