Monitor Description
WARNING: This page is about a different car, the 2004 Toyota Corolla. However, it is still accessible from the selected car via links, so may be relevant.
The ECM estimates the engine coolant temperature (ECT) based on starting temperature, engine loads, and engine speeds. The ECM then compares the estimated ECT with the actual ECT. When the estimated ECT reaches 75°C (167°F) the ECM checks the actual ECT. If the actual ECT is less than 75°C (167°F), the ECM will interpret this as a fault in the thermostat or engine cooling system or thermostat and set a DTC.