I am not sure but something clicks in my mind that even though there is usually a delay in power going to the 120 vac part of your coach, the genny starts producing immediately and that the outlet on the genny receives power immediately.
Doug may step in here soon and will know for sure.
The codes are not absolute, mine were all low oil pressure, but the problem was a faulty rotor/stator assembly.
You may be able to check the voltage at the generator by plugging in anything that gives a voltage reading immediately. My DMMs don't so I use a three light outlet checker.
It may be worth a try.