I've tested a 2014 tune on my 2017. No issues. DEF works fine. Although I warn people when they ask that DEF usage might be slightly higher than normal. However, I was tuned since 1k miles and DEF was disabled in my tune so there could be other variables at play.I’d you are referring to my post, the issue wasn’t the def gage, but the lack of my truck having the def quality sensor and the newer ECU was looking for it. You are talking about the opposite configuration. I do not recall anyone trying it.
My best guess is that you will be fine putting the 2014-15 ECU in a 2016. I think the ECU would ignore the extra module. Won’t really know unless someone tries...or maybe GDE has some insight.
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