Another Onan 4000 ky problem

[Rdy1]

I have a Onan 4000 ky k series. It is in my RV and is 7 years old with very low hours. It runs and starts great but once it runs for about 15 minutes it shuts down and gives a 12 code over voltage. You can start it again with no load and once load is put on it shuts down. You can let it rest for 1/2 to one hour and will do the same sequence. I can start it with no load and put the load on it and I can see it quickly spikes on the volt meter to 157 volts otherwise it will run with 120 to 121 volts. It is not specific appliance. It can be the refrigerator or the air conditioner or even the AC to DC converter. I just don’t want to replace the control module in it if that is not it. I just bought the RV last year.