Yes, BUDS would be the best diagnostic tool, but the FADEC connection to the Garmin G3X does a decent job on simple codes. In this case it’s telling him he has an oil temp sensor fault. So a simple visual check of the wiring as Roger suggested is a good start. Might find a loose connection at the oil temp sensor.
And Roger, I agree that 20 times unplugging the ECU connectors is a lot in the lifetime of the engine, probably 5 times is even unlikely. I’ve never unplugged mine in 400 hours, but I think folks should be aware so they don’t do it 10 times trying to trouble shoot a single problem. And it’s still a good idea to log it, or maybe that’s just my OCD?