Generac guardian rv generator starts and runs but after a couple minutes the power stops.....generator still runs??

SOURCE: Generac Guardian 17.5KW Generator dies

If this is one of the big "taco cart" portables you need to check that the vent on the gas cap is open when you're running the engine. In the center of the gage on the gas cap is a little knurled knob, turn it counter clockwise (lefty loosey), about a half turn or so and run the generator.
If that doesn't solve your problem add to it here, otherwise please give me a rating I'm trying to build a little credibility here and could use the help.
Carl

SOURCE: Generac Guardian 15kW Generator

That sounds just about right, if the relay contacts get welded together it sometimes takes out the driver on the printed circuit board. As you found out, 12vdc from 23 to 194 makes the transfer switch move to the Generator position, relay not energized makes the ATS move to the Normal position.

You can make a nice test function by installing a 10 amp contact switch in series with either the N1 or N2 terminals. When the switch is open the generator thinks the Normal power has failed.

Regards,
Carl

SOURCE: my generac guardian RV ran for a few hours then

Check for low oil or over temp.

SOURCE: Generac Guardian 15 kw overspeed fault

Did you remember to set the overspeed shutdown threshold on the control board?

SOURCE: My generac 40g rv generator will start fine but no

It may be demagnetised. If you turn off the generator before unplugging the load this may happened. Try to put a strong magnet (like those from loudspeakers) in contact with the body of alternator. I do this in the past and it work.If you do not know how to do this ask an electrician, he can help you .