Controller displays MAINTENANCE DUE, SERVICE DUE, or similar reminder; generator still runs but service is overdue.

Safety first: Place the controller in OFF, open the main breaker, and allow the engine to cool before servicing.

• Perform oil and filter change: Drain engine oil, replace the oil filter, and refill with Guardian-approved oil to the correct level.
• Replace air filter and spark plugs: If due, install a new air filter and spark plugs per the maintenance schedule.
• Inspect battery and terminals: Clean and tighten battery connections and verify charger operation.
• General inspection: Check for fuel leaks, loose fasteners, and damaged wiring inside the enclosure.
• Reset maintenance timer: Use the controller menu to reset the maintenance interval after completing service.