Detection Condition

WARNING: This page is about a different car, the 2003 Mazda Protege5 and 2003 Mazda Protege. However, it is still accessible from the selected car via links, so may be relevant.

If ECT signal never exceeds 160°F (71°C) after engine start for specified period, PCM determines coolant thermostat is stuck open.

Monitoring Conditions

Difference between engine coolant temperature at engine start up and minimum intake air temperature readings is less than 43°F (6°C).
Intake air temperature is more than 14°F (-10°C).
Vehicle speed is more than 5.9 MPH.

This is an intermittent monitor. MIL is illuminated when PCM detects malfunction condition in 2 consecutive drive cycles. Pending code is available if PCM detects malfunction condition during first drive cycle. Freeze frame data is available and DTC is stored in PCM memory.