Malfunction Threshold

Malfunction determination 1:

If the difference between the current measured coolant temperature at the radiator (ECT 2) and the initial coolant temperature at the radiator (ECT 2) is at least 46 °F (8 °C) when the calculated coolant temperature at the engine (ECT 1) reaches 159 °F (71 °C), a malfunction is detected (thermostat stuck open); or if the coolant temperature at the radiator (ECT 2) only reaches 73 °F (23 °C), a malfunction is detected (thermostat malfunction).

Malfunction determination 2:

When the calculated engine coolant temperature (ECT 1) reaches 158 °F (70 °C) before the measured engine coolant temperature (ECT 1) reaches 158 °F (70 °C), a malfunction is detected.