P0128 came back after replacing t-stat

Well code 128 is for the engine running too cool. Which is usually a thermostat problem. But it could be the coolant temp sensor.
You may have a different sensor for the gauge and for the computer.
Code 442 is for a small leak detected in the EVAP system. It can be a faulty gas cap, but since you have replace the cap, its probably a hose or gasket. The computer vents the gas tank to the vapor canister when the engine is running. It checks gas tank pressure to make sure all valves are closed when you turn the truck off.

First off when did this start? Was it prior to the Thermostat replacement or after? What was the purpose of relacing the tstat?

From my experience use only a high quality t-stat that maintains a constant temp. is the best solution, it's easy to try and save a few bucks I'm just as guilty as the next guy however I've had many years of experience in the automotive field, throughout the years I've replaced hundreds if not thousands of t-stats and all are not even close to created equal. My opinion is not to go to the big box stores to purchase an off branded t-stat these t-stats open very inconsistantly and tend to have temps that fluctuate greatly. Commonly these economy t-stats are rated at say 195 degrees however they tend to snap open and closed very fast and erratically causing the temp to suddenly drop and then snap closed when the coolant falls below the opening temp. And again reopen not at the 195 always but sometime not opening until say 205 or 210 and then again snaping open and the cycle continues. Buy a premium t-stat and you'll be glad you did.

P0128 is a code for engine temp below regulated temp. It usually sets when the t-stat goes bad and is either broken or stuck open. Either of which can happen on the sentra. Replace the t-stat (especially if you have noticed that your temp gauge has been reading a little low) and that should solve the problem.

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www.obd-codes.com/trouble_codes insufficiant coolant temp for stable operation thats an uncommon one. unless u have no thermostat or to cool of one u shouldnt have that code again usualy comes on when a seensor is wrong, bad but not out of range for the computer to show coolant temp sensor. very uncommon. if it comes back on again then check ur sensor and wires also it may have just been ur thermostat stuck open. u may want to put a new one in it it runs cold. u should be able to tell by the gauge if ur temp is ok. most gm engines have two sensors. one for the computer and one for the gauge. not always though.

Fix the P0128 code first. Usually a bad thermostat

have a 2004 ford f150 with a 5.4L. While the truck would sit and idle my temp gauge would go to zero and the check gauge and check engine light would come on. Ran the codes and got P1289. Cleared the codes and truck would do fine for a few days and then it would happen again while sitting and idling. I replaced the CHT sensor and cranked the truck. The check gauge light can on and got the P1289 code. Replaced the CHT again(thinking the new one was bad) and cleared the codes. Cranked the truck again and it did the same thing. Cleared the codes and the check gauge light and check engine light would come back on with the motor running. When the motor is warmed up, I turned on the key on without cranking the motor, the temp gauge works, when the motor is cranked and running, the temp gauge goes to zero and the the ckeck gauge light on back on and gives the P1289 code. Does any one have any ideas on what to do

I think your on the right track. I don't recall if this vehicle has electric or belt driven cooling fans, but if electric (and it's real cold where you are located), make sure they are shutting down when they should.

PO128 is coolant thermostat(coolant temperature below thermostat regulating temperature). check the coolant level first. PO 304 is a misfire in the number 4 cylinder. hope this helps if you need more help get back to me, please rate my fix as i strive to be the best Thanks Ray

firstly, check coolant, add to required level. a fluctuant temp gauge usually means there is a migrating air pocket in the system somewhere. the question is, is this a new air pocket due to currently leaking coolant or is it a pocket leftover from the t-stat replace way back when that was never completely bled out? if the coolant already seems at the required level, then the system needs to be bled again. if this does not solve it, then i would again suspect the t-stat

It could be a faulty thermostat. Did it do the same thing before u replaced the t-stat? It sounds like it's sticking closed, then all of a sudden it opens, coolant flows correctly. I'd consider changing it again. Check to make sure parts store is giving u the correct temperature thermostat also. Maybe it's too high for your Ford, delaying the opening.