Controller maintenance menu indicates SPARK PLUG SERVICE; engine may misfire or start hard.

Safety first: Turn the controller to OFF, open the main breaker, and disconnect the negative battery cable. Allow the engine to cool.

• Remove spark plugs: Disconnect plug wires and remove plugs with the correct socket.
• Inspect condition: Replace plugs that are worn, cracked, or heavily fouled. Use only Guardian-specified spark plugs.
• Set gap: Check and adjust the gap to the specification in the Guardian manual.
• Reinstall and torque: Install plugs by hand to avoid cross-threading, then torque to spec and reconnect plug wires firmly.
• Reset reminder: Use the controller to reset the spark plug maintenance interval.