DTC P0128:00 [MZI-3.7]: Notes

WARNING: This page is about a different car, the 2009 Mazda 6. However, it is still accessible from the selected car via links, so may be relevant.

DETECTION CONDITION & POSSIBLE CAUSE

DTC P0128:00	Coolant thermostat (coolant temp below thermostat regulating temperature)
DETECTION CONDITION	P0128:00 indicates that the thermostat monitor has not achieved the required engine operating temperature within a specified amount of time after starting the engine.
POSSIBLE CAUSE	Low engine coolant level Inoperative CHT sensor Leaking or stuck-open thermostat Insufficient warm up time PCM malfunction