Not sure of the exact model you have but here is a link to a service manual for Onan RV generators. Even if not your exact model the steps to trouble shoot your problem would be the same.
https://www.cumminsonan.com/www/pdf/manuals/983-0501D.pdf
(Not sure how to make a Clicky so you will have to copy and paste the address)
On my Onan 5500 Fault Code 36 normally indicates a fuel issue. Check the fuel lines for cracks or loose clamps. Change the Gennie fuel filter and check the genie fuel pump.
To me this sort of issue is one of the benefits of owning a motorhome. There is always something to adjust, repair or diagnose.
Good Luck and Safe Travels!
