if it's a generac Quiet Pack 75D it could be a faulty oil pressure sensor. Depending on how it's mounted it might not be possible to access while in the motorhome. there is a way to bypass it by moving a wire. I had to do this to mine as it would run then shutdown, and would continue to do that...
very common problem on the generac gen sets.
1998 Winnebago Chieftain WKL36L Diesel Pusher.
5.9 24V Cummins, 6 Speed Allison
Toad: 2014 Grand Cherokee, Limited, diesel