P0128 Coolant code on the Forte 2.4L

A word of advice: there is a TSB floating around that covers various Hyundai/Kia vehicles regarding a P0128 code. Apparently, the ECU's cooling system logic gets easily confused if the system has anything more than a 50/50 antifreeze mix in the system. Past 50% straight coolant, and the computer can get confused.

I have personally run into this after doing a coolant flush on said vehicles. If the ratio isn't spot on, a code you shall see.

Does the TSB provide a fix? Or is only using exactly 50-50 mix their "fix"?
2-ethyl hexanoic acid..... not something I care for. Pretty sure the Hyundai coolant is different.

Feel free to post the p0128 TSB. There were plenty of defective thermostats and even a software patch for some models.

Am glad OP fixed his issue.
I couldn't find the TSB... so that may have been an old Identifix tip I read at some point. Either way, I've fixed several just by doing a flush and making sure the mix is 50/50.
There is a bunch of P0128 references similar to this one:

I know the issue has been solved by @1SX but maybe the source for the screenshot can help others with DTC's. I noticed some solutions/view solutions are not free.
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