The controller shows AL03 / Overspeed, and the generator stops immediately after a start attempt.

Safety first: Disable automatic start (set the controller to OFF), open the generator output breaker, and disconnect the battery negative before inspecting engine components.

• Inspect speed sensor: Locate the magnetic pickup sensor near the flywheel ring gear on the Kohler-SDMO engine. Check for loose mounting, damaged cable, or metal filings on the sensor tip. Clean the tip and ensure the correct air gap per the engine manual (typically 0.5–1.0 mm).
• Check governor actuator: On sets with an electronic actuator, inspect the actuator linkage to the fuel injection pump. Ensure it moves freely and is not binding. Check the actuator electrical connector for corrosion or loose pins.
• Verify controller settings: Using the APM303/APM403 menu, confirm the rated speed (e.g., 1500 or 1800 rpm) and overspeed threshold are correctly configured for the generator model. Do not change parameters unless you have the configuration data.
• Mechanical linkage: Manually move the fuel rack or throttle lever on the injection pump (engine off) to ensure it is not stuck. Lubricate external linkages lightly if stiff.
• Test run: Reconnect the battery, clear AL03, and start the generator while monitoring engine speed on the controller. If overspeed persists, stop immediately.

Persistent overspeed alarms may indicate a failing governor actuator or incorrect fuel pump settings—these should be handled by a qualified diesel technician.