Detection Condition

WARNING: This page is about a different car, the 2003 Mazda MPV and 2002 Mazda MPV. However, it is still accessible from the selected car via links, so may be relevant.

PCM monitors ECT signal after start up for a specified time. If ECT signal never exceeds 160°F (70°C), PCM determines coolant thermostat is stuck open and DTC is set. If difference is more than specified, DTC P0126 is set. PCM also monitors MAF, IAT and VSS signals and calculates radiator's heat radiation ratio while following monitoring conditions are met.

Monitoring Conditions

ECT at engine start: Less than 95°F (35°C).
IAT: More than 14°F(-10°C).
Difference between ECT at engine start and minimum IAT: less than 43°F (6°C).
Vehicle speed: more than 5.9 MPH.

If calculated value exceeds threshold, PCM determines coolant thermostat is stuck open and DTC P0128 is set. This is an intermittent monitor. MIL illuminates if PCM detects malfunction in two consecutive drive cycles.