Onan 4000 issue

Could be a lots of issues, short, bad breaker, loose or bare wire, ect. If I read your post correct you know the generator is working, and its just the one circuit.
I would start looking at the breaker, starting with that breaker. make sure the wire that's attached to the breaker is tight. and that the breaker is fully seated. then follow the circuit, checking anywhere it could touch anything , where does the wire go? what does it connect to? an outlet, switch, or appliance.

It seems that the problem is that you don't know what that breaker really serves; what it's purpose is. To find that out, you need to see your dealer or contact Coachmen.....unless another owner with the same model shows up here.

The symptoms do sound a little strange.
What is your shore power cord "doing" when this happens ?? That is, is it plugged into anything ?

Yes, shore cord is connected to dedicated generator outlet box and I can't figure out what's the purpose of the 15 amp house breaker since everything seems to be working fine but i will check succested areas. Thans!!

Is the breaker labeled "generator" or just "gen"? "gen" would probably mean "general purpose," i.e. outlets that are not dedicated to a specific device and (probably) are not protected by the GFCI.

If it's labeled "generator", and actually associated somehow with a generator, there's something quite odd with your RV's wiring. If it's used, maybe a previous owner put in some sort of a backfeed inlet to hook up a portable generator or an inverter. If so, from the sounds of things, it should be removed with extreme prejudice as it sounds as though it's dangerously set up without any form of appropriate transfer switch.

It is labeled as Gen, so you are probably right. Iam original owner of this unit and no alterations have been made for it. So could it have something to do with charging system?

justgo wrote:
It is labeled as Gen, so you are probably right. Iam original owner of this unit and no alterations have been made for it. So could it have something to do with charging system?

Maybe. What's your battery voltage with the gen running ? Above 12.6 ??
Does your owners manual not mention anything about that breaker ?

I'd be interested to see what happens with the gen running and the shore power cord unplugged and then that breaker switched ON.
I don't know why I say that exactly, just curious.

I REALLY think you need to see your dealer.
Not knowing why that is happening would make me VERY nervous.

Just quick update, I took camper to service and it was bad converter and battery, now it seems to be working great! Thanks for help guys!

Thanks for coming back and letting us know.