Our Onan generator failed with about 23 hours on it. The secondary codes were 13 and 12 - separated by a brief period of normal operation.
The cause turned out to be a failed voltage regulator which is an integral part of the PC board in our unit. The part cost was about $300 and it was replaced in about a half hour by a local authorized technician. The Cummins warranty is good for 3 years and our 24M was purchased a year ago March so the cost to us will be small if anything - aside from not being able to use our electric K-cup coffee maker while we were traveling which was no big deal.
Just got back from a 3-week trip to a family reunion.