Last night after filling my truck up with 87 octane (had been running 92) tried returning the truck to stock (didn't have an 87 octane tune on my Xcal II). Programming got to about 70% and then the Xcal flashes "Programming Failed Press Select" so I did. Tried to start, but truck wouldn't start up. So I tried it again and the second time I was able to return the truck to stock and start it up. Never had a programming failed message before. Anyone know what would cause this?

 

PCM probably saw a fluctuation in battery voltage and terminated the programming.

 

Thanks