Why generators show "overspeed": 3 documented causes and brand-specific fixes, compiled across 7 manufacturers.
Bad overcrank fault circuit; bad actuator and mixer function; bad flywheel/crank sensor; bad controller
2 brands- Generac: Test 96 – Test Overcrank Fault Circuit; Test 68 – Test Actuator and Mixer Function; Test 97 – Check Flywheel/Crank Sensor; Identify new fault indicated; Replace or readjust; Replace controller
- Nexus: Test 96 – Test Overcrank Fault Circuit; Test 68 – Test Actuator and Mixer Function; Test 97 – Check Flywheel/Crank Sensor; Identify new fault indicated; Replace or readjust; Replace controller
Fault Code 171 present; Engine reverse powered (motoring of engine / reverse power); Alternate fuel source present; Incorrect rpm reading
1 brand- Cummins/Onan: Identify the reason for the overspeed; Check for Fault Code 171; Check for motoring of engine (reverse power); Check for alternate fuel source; Check engine rpm with service tool monitor; Clear fault codes; Disable the fault code; Clear the inactive fault codes
Cold engine (no heaters); Single step large block load removal; Fault simulation has been enabled with InPower; Fault threshold is incorrectly set with InPower; Monitor the engine RPM using InPower; The electronic governor actuator is defective
1 brand- Cummins/Onan: Overspeed can occur when starting a very cold engine. Clear the fault and restart the generator set; Clear the fault and restart the generator set; With InPower, verify that the fault simulation is not enabled for the coolant sensor. If you do not have InPower, remove battery power from the control to disable fault simulation overrides; Reset the threshold to the highest allowable setting. Determine the required operating range before adjusting the threshold; If the RPM is not correct, refer to Fault Code 121 for corrective action; Check for binding in the actuator assembly of the injection pump. Disassembly of the injection pump may be required to inspect/repair O-rings, pump, etc. Refer to engine service manual.