I have a 2013 cruze 1.8, I am getting code p0128, and on the side there is a p/d. anyway it is code for temp is running cooler . I have replaced the thermostat and heat sensor and still getting it. thermostat has been replaced 3 times, any ideas my mechanic is also baffled, along with parts store.
with scanner confirm ECT. Then compare to Atips suggestion. There are 2 ECT sensors 1 in radiator, an other at T'stst. disable one to confirm which supplies this reading. Other is likely gauge. Did you get T'stat from GM?
Gauge would be one wire. PCM would be 2 or 3 wire, but your one could be totally different as 2013. Some vehicles like ford has one for PCM and Gauge and 2nd one for radiator fan to kick on. All vehicle are different animals.
I would check live data of ECT engine coolant temperature and confirm with laser gun thermometer. https://www.obd-codes.com/p0128