Cummins/Onan QSB5-G3 NR3 Engine

Shared across brands: Cummins/Onan, Magnum, Terex

How to read your Cummins/Onan engine serial & model number →

• Voltage does not come up to the rated voltage
  Cause: Internal problem with the generator end
  Fix: Check for even reading across the lines, if they are not this would mean you probably have a problem with the wiring of the switch or generator. If the generator voltage reads correctly, contact the TEREX service department.
• Uneven reading between the legs when applying 24 volts to the field wires
  Fix: Recheck your wiring connections. After you have the field wire connected start the unit again and check your output voltage. It may still be necessary to flash the fields to restore residual voltage.
• TROUBLE LIGHT on CONTROL PANEL is illuminated
  Cause: Broken fan belt
  Fix: Inspect fan belt and replace as needed
• OVERSPEED OR UNDERSPEED SHUTDOWN
  Cause: Engine speed is above or below 60.0 Hz.
  Fix: Disconnect loads and adjust engine speed as needed based on manual instructions.
• OVERCRANK SHUTDOWN
  Cause: Engine will not start.
  Fix: Check fuel level, fuel pump operation, air filter for blockage. Refer to manual for additional troubleshooting.
• No generator output voltage
  Cause: Circuit breaker tripped
  Fix: Reset circuit breaker
• Malfunction discovered
  Fix: Identify symptoms, troubleshoot, perform repair, return to service
• LOW OIL PRESSURE SHUTDOWN
  Cause: Oil pressure is less than 20 psi (138 kPa).
  Fix: Check oil level, inspect for leaks, and check the oil pressure sender.
• Low generator output voltage
  Cause: Voltage adjustment set too low
  Fix: Adjust voltage potentiometer
• LOW FUEL LEVEL SHUTDOWN
  Cause: Fuel level in the tank is low or fuel lines are running dry.
  Fix: Check and refill the fuel level. Inspect for leaks and check the fuel level sender.
• Low engine speed
  Fix: Call TEREX Service
• LOW COOLANT LEVEL SHUTDOWN
  Cause: Coolant level in the radiator is low.
  Fix: Check coolant level, inspect hoses, engine block, water pump for leaks, and check oil for coolant contamination.
• High generator output voltage
  Cause: Voltage adjustment potentiometer set too high
  Fix: Adjust potentiometer
• High engine speed
  Fix: Call TEREX Service
• HIGH COOLANT TEMPERATURE SHUTDOWN
  Cause: Coolant temperature is 230°F (110°C) or more.
  Fix: Check coolant level, remove any blockages, inspect hoses and components for leaks, check water pump belt tension, and load the unit to prevent overheating.

Compiled from service & troubleshooting documentation across every generator set that uses the Cummins/Onan QSB5-G3 NR3.

Pooled from every document that names this exact engine — confirm the interval and part number against your unit's serial number.