I have 2008 Dakota 4.7. Chk engine light comes on throws code 128. Have replaced thermostat and sensor, light still comes on and later goes off by its self. Never has over heat....Can not figure what replace next.

 

If I am correct and if not someone please correct me, but a PO128 could mean the engine is not reaching normal operating temperature. If that is the case it is possible the fan is running too much/too early. Also have you checked the coolant level?
Some more info that may help is how long of driving does the light come on and how long before it goes off?

 

Not an electric fan. Coolant level is proper and new.

 

I just looked at Alldata, and there's a huge diagnostic tree to deal with P0128. Here's the summary chart.

 

my apologies i just wanted to seek guidance. I have been struggling getting this p0128 code out. Originally I had p0128, and other emission codes. I replaced the EVAP hoses and replaced the coolant temp thermostat (i replaced the thermostat about 3 or 4 years ago). I disconnected the battery and everything cleared except a evap code. I replaced the gas cap and all the evap codes stayed off but the P0128 code is back on. I checked the PCV but that is fine (cleaned it up a bit but still rattles). Any other ideas, i would appreciate the assistance?