Monitor Description
WARNING: This page is about a different car, the 2004 Lexus ES 330. However, it is still accessible from the selected car via links, so may be relevant.
The ECM estimates the coolant temperature based on starting temperature, engine loads, and engine speeds. The ECM then compares the estimated temperature with the actual engine coolant temperature (ECT). When the estimated coolant temperature 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 engine cooling system thermostat and set a DTC.