There is a Start/Stop/Prime switch on the generator itself behind the access panel. Press Start there. If you see 3 flashes from the switch, that’s a service code fault. Press Stop/Prime on the control switch once to have the actual 2 digit service fault code flash. It’s 2 sets of blinks with a pause in between. You need to count the blinks to get a two digit number.. Then look up that code in the Troubleshooting section of the Cummins Onan Generator HGJBB Operator Manual section 6.2 “Fault Codes”.