Generator shuts down shortly after start, controller shows E004 Overspeed

Safety first: Overspeed can cause catastrophic mechanical failure. Do not repeatedly attempt to start the unit until the cause is identified. Isolate the generator from the load and secure all covers.

• Check speed sensor: Locate the magnetic pickup or speed sensor near the flywheel or timing gear. Inspect for metal debris on the sensor tip and clean carefully. Ensure the air gap to the gear is within specification.
• Inspect wiring: Trace the speed sensor cable back to the Atlas Copco controller. Look for crushed sections, oil‑soaked insulation, or loose connectors. Repair or replace damaged harness sections.
• Verify controller settings: In the controller configuration (service level), confirm the rated engine speed (e.g. 1500 or 1800 rpm) and overspeed threshold are correctly set for your model. Only qualified personnel should change these parameters.
• Check fuel actuator/governor: On electronic engines, ensure the fuel actuator linkage moves freely and is not sticking at high fuel positions. On mechanical governors, inspect the linkage and return springs.

If the engine audibly races before shutdown, do not run again until a professional Atlas Copco technician inspects the governor and fuel system.