Cummins/Onan NT-855-G2 Engine

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

• The FAULT 1 or FAULT 2 fault lamp lights. Engine shuts down immediately, engine runs for several seconds and then shuts down, or engine continues to run. FAULT 1 or FAULT 2
• SWITCH OFF lamp flashes.
  Fix: Indicates Run-Stop-Remote switch is in the Stop position which will prevent automatic Starting. Moving the Run-Stop-Remote switch to the Remote position will stop the lamp flashing and enable automatic starting.
• No AC output voltage.
  Cause: Voltage regulator is inoperative.
  Fix: Refer to Initial Start and Checks, and Adjustments sections of your Installation Manual for voltage check and adjustment procedures. Contact your distributor if voltage build-up is still a problem.
• LO FUEL lamp lights. Engine continues to run.
  Fix: Indicates diesel fuel supply is running low. Check fuel supply and replenish as required.
• Green RUN lamp does not light following engine start-up.
  Cause: Indicates possible Start/Disconnect relay failure.
  Fix: Contact your distributor for assistance.
• Engine will not crank.
  Cause: Indicates possible fault with control or starting system.
  Fix: A. Fault lamp on. Correct fault and reset control. b. Poor battery cable connections. Clean the battery cable terminals and tighten all connections. c. Discharged or defective battery. Recharge or replace the battery. d. Contact your distributor for assistance if none of the above applies.
• OVERCRANK lamp lights and engine stops cranking.
  Fix: A. Check for empty fuel tank, fuel leaks, or plugged fuel lines and correct as required. Engine runs, shuts down, and LO OIL PRES lamp lights. b. Check for dirty fuel filter and replace if necessary (see MAINTENANCE section). c. Check for dirty or plugged air filter and replace if necessary (see MAINTENANCE section). d. Refer to step 5. e. Reset the control and restart after correcting the problem. Contact your distributor for service if none of the above applies.
• LO FUEL lamp lights. Engine shuts down and LO OIL PRES lamp lights.
  Fix: Indicates engine has run out of fuel. Check fuel level and replenish as required.
• LO ENG TEMP lamp lights.
  Fix: Indicates engine coolant heater is not operating or is not circulating coolant. Check for the following conditions: a. Coolant heater not connected to power supply. Check for blown fuse or disconnected heater cord and correct as required. b. Check for low coolant level and replenish if required. Look for possible coolant leakage points and repair as required. c. Contact an Onan Dealer or Distributor if none of the above.
• Fault lamp lights but no fault exists.
  Fix: The monitor board or a sensor may be at fault. Contact an Onan Dealer or Distributor for service.
• Engine runs and then shuts down, OVERSPEED lamp lights.
  Fix: Indicates engine has exceeded normal operating speed. Contact your distributor for service.
• Undedicated fault. May be factory programmed as a shutdown or non-shutdown, and as a timed or non-timed (normally set for timed shutdown). FAULT 1 (red)
  Cause: @ FAULT 1 (red) an undedicated fault. May be factory programmed as a shutdown or non-shutdown, and as a timed or non-timed (normally set for timed shutdown).
• The engine does not start.
  Cause: The starter will disengage after a specified period of time and the control will indicate an overcrank fault. Generator sets with the standard overcrank control will crank continuously for up to 75 seconds before disengaging the starter. Generator sets with the cycle cranking option will crank for 15 seconds and then stop for 15 seconds until 3 cycles have been completed.
  Fix: Place the Run-Stop-Remote switch in the STOP position and momentarily depress the Reset switch. Wait two minutes for the Starter motor to cool and then repeat the starting procedure.
• The engine does not run after a second attempt at Starting.
  Fix: Refer to the TROUBLESHOOTING section.
• Starter has been locked out because of excessive cranking time
  Cause: @ OVERCRANK (red) indicates the starter has been locked out because of excessive cranking time.

Compiled from service & troubleshooting documentation across every generator set that uses the Cummins/Onan NT-855-G2.

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

Parts cataloged across all variants of this engine family — verify the exact part fits your specific variant and serial number before ordering.