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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.

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The most likely cause is the thermostat. The on the road temp is the clue, it should be at the thermostat open temperature which is specified to be 180 deg F. This is the lowest temperature that should be seen on a road test if the thermostat is working normally.

It is possible that the sensor is reading 20 deg F low but it is not at all a common problem.

Check also if this TSB 18-006-11 has been performed. It is for reprogramming of the PCM for this code.

  • Is 180 the correct temperature? When I look up the thermostat for the vehicle at napa, the compatible parts say 203 degrees. – Zack Dec 6 '17 at 13:27

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