Cummins/Onan LRG-423 (Turbocharged) Engine

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

• The OVERLOAD lamp lights. Engine shuts down.
  Fix: Locate the source of overload and correct as necessary. Manually reset breaker to reconnect the load to the generator.
• The O/U VOLTAGE lamp lights. Engine shuts down.
  Fix: Contact an authorized service center for service.
• SWITCH OFF lamp flashes.
  Fix: Indicates Run/Stop/Remote switch is in the Stop position which will prevent automatic starting if an automatic transfer switch is used. Move the Run/Stop/Remote switch to the Remote position for automatic starting.
• PRE HET/LOP lamp lights. Engine continues to operate.
  Cause: Indicates engine has begun to overheat and engine temperature has risen to approximately 205°F (97°C) or coolant level is low.
  Fix: A. Reduce load if possible by turning off non-critical loads. b. Check cooling air inlets and outlets and remove any obstructions to airflow.
• OVERCRANK lamp lights and engine stops cranking.
  Cause: Indicates possible fuel system problem.
  Fix: A. Check for empty fuel tank (LPG Vapor), fuel leaks, or plugged fuel lines and correct as required. b. Check for dirty fuel filter and replace (if installed on fuel line). c. Check for dirty or plugged air filter and replace if necessary (see Maintenance section). d. Reset the control and restart after correcting the problem. Contact an authorized service center for service if none of the above.
• No AC output voltage.
  Cause: Field breaker is tripped. Reset breaker. Contact an authorized service center if voltage buildup causes breaker to trip.
• LO OIL PRES lamp lights. Engine shuts down.
  Cause: Indicates engine oil pressure has dropped to 14 psi (97 kPa).
  Fix: Check oil level, lines and filters. If oil system is OK but oil level is low, replenish. Reset control and restart. Contact an authorized service center if oil pressure is not in the range of 40 to 65 psi (275 to 448 kPa).
• LO FUEL pressure lamp lights.
  Fix: Indicates interruption of natural gas supply. Connect to a propane fuel supply (if not already connected). Move the select
• HI ENG TEMP lamp lights. Engine shuts down.
  Cause: Indicates engine has overheated (engine temperature has risen above 215°F/102°C) or coolant level is low.
  Fix: A. Check coolant level and replenish if low. Look for possible coolant leakage points and repair if necessary. b. Check for obstructions to cooling airflow and correct as necessary. c. Check for a slipping fan belt and tighten if loose. d. Reset control and restart after locating and correcting problem. Contact an authorized service center if none of the above.
• Green RUN lamp does not light following engine startup.
  Cause: Indicates possible Start/Disconnect relay failure.
  Fix: Test light with LAMP TEST position on switch. Contact an authorized service center for assistance.
• Fault lamp lights but no fault exists. Engine gauges show oil pressure, engine temperature, and frequency (speed) are within normal limits.
  Cause: The monitor board or a sensor may be at fault.
  Fix: Contact an authorized service center for service.
• Engine will not crank.
  Cause: Indicates possible fault with control or starting system. Check for the following conditions:
• Engine runs and then shuts down, OVERSPEED lamp lights.
  Fix: Contact an authorized service center for service.
• Engine fails to start or starts, runs and then stops
  Fix: Refer to Troubleshooting charts in the Operator's Manual
• The engine does not start after three full cranking cycles.
  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.

Compiled from service & troubleshooting documentation across every generator set that uses the Cummins/Onan LRG-423 (Turbocharged).

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.