Meadows

I know this is an old post, but I just rebuilt a 14 Silverado that was a total. I used a engine / chassis from a 15 Silverado that was a rollover but good straight frame. I used the 14 engine computer since it worked with the key from the 14 cab. I have the code for the ethanol sensor because the 15 frame didn't use it. My question is how to reprogram the ecm, or can it be to eliminate this code from staying on. Or how could I add the sensor so the computer would see it. I tried the 15 ecm and reprogramming the key but it didnt work.?? It put it in theft mode. Do you have to use a new chip key for the key program to work? I was trying to reprogram the original key? Runs perfect other than the check engine light on. I'm not in an emission county so doesnt bother me til it's time to sell. Thanks