Small Engine Troubleshooting Problems? Ask a Mechanic Now.
Code 27 is AC Voltage Sense Lost.
You need to check and make sure it is putting out 120V.
Then this unit will need to be taken to an Onan dealer that has a Break Out tool. Using a Break Out tool is the only way to keep the unit running long enough to test it out.
A Break Out Tool is about $1000.