今天很巧的一个sotry: 2003 Mazda MPV coolant system multiple problems:
1. T- sensor gone: give a coolant temperature DTC code, scanner found coolant temperature always stays at 50 deg-c
2. rad. fan always running at full speed, even at key on engine off.
3. After changing T sensor, radiator lower hose cold after idling half hour, with higher hose hot, and coolant temperature reaches and stablized at 95 deg-c. This is a firm sign of thermostat stuck close but not overheating since fan crazy running.
For fan always running, owner said it has been like that for a long time. After diagnosis, it is the fan control module failure, which is also a ECM controled one like yours.