I had the same issue, ran until you let go of the start button.
once you let go of the button and it shuts down, it will blink, push again and you'll get a secondary code: a number of blinks, a pause and a second set.
Mine had the following: 3 blinks, then 4 blinks <pause> 5 blinks. I emailed cummins and they told me what the code 3, 45 meant.
Mine basically had to have a bit of work done, including a new wiring harness.
good luck. Get the codes, it may give you a good starting point (after you've checked the oil level and make sure your gas tank is greater than 1/4 full)
2016 Tiffin Allegro 32 SA
2015 Chevy Malibu LTZ Toad