My 2011 Town and Country is reporting P0128 intermittently. If I understand correctly, this error code points to either the thermostat, the ECT sensor, or a computer module.
When driving normally, the reported temperature stays around 160. When I let the van idle in the driveway, it will warm up to 200. When I start the cold engine, the heater will blow warm air within a few minutes and the large hose coming out of the radiator does not get particularly warm.
Should I replace the thermostat first or the ECT sensor?
The fact that the heater works normally suggests that the problem is the sensor; however,
The sensor seems to report reasonable temperatures (beginning at <100 and slowly warming up to 200 when idling). Also, the fact that the car cools to 160 when driving down the road seems to point to the thermostat.