Cummins/Onan LRG-423 Engine

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

• Engine will not crank
  Cause: Fault lamp on
  Fix: Correct fault and reset control
• The OVERLOAD lamp lights. Engine shuts down
  Cause: Load exceeds generator current rating, the breaker will trip preventing the generator from being overloaded
  Fix: Locate the source of overload and correct as necessary; manually reset breaker to reconnect the load to the generator
• PRE HET/LOP lamp lights. Engine continues to operate
  Cause: Engine has begun to overheat and engine temperature has risen to approximately 205°F (97°C) or coolant level is low
  Fix: If generator is powering non-critical and critical loads and cannot be shut down: reduce load if possible by turning off non-critical loads; check air inlets and outlets and remove any obstructions to airflow
• LO OIL PRES lamp lights. Engine shuts down
  Cause: 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)
• The O/U VOLTAGE lamp lights. Engine shuts down
  Fix: Contact an authorized service center for service
• SWITCH OFF lamp flashes
  Cause: Run/Stop/Remote switch is in the Stop position which will prevent automatic starting if an automatic transfer switch is used
  Fix: Move the Run/Stop/Remote switch to the Remote position for automatic starting
• PRE HET/LOP lamp lights. Engine continues to operate. PRE HET/LOP
  Cause: 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 air inlets and outlets and remove any obstructions to airflow. 2A. Indicates engine oil pressure has dropped to 20 psi (137 kPa). If generator is powering critical loads and cannot be shut down, wait until next shutdown period and then follow step 4. If engine can be stopped follow procedure in Steps 3 and 4.
• OVERCRANK lamp lights and engine stops cranking. or Engine runs, shuts down, and LO OIL PRES lamp lights
  Cause: Possible fuel system problem
  Fix: Check for empty fuel tank (LPG Vapor), fuel leaks, or plugged fuel lines and correct as required; Check for dirty fuel filter and replace if necessary (see Maintenance section); Check for dirty or plugged air filter and replace if necessary (see Maintenance section); Reset the control and restart after correcting the problem. Contact an authorized service center for service if none of the above
• OVERCRANK lamp lights and engine stops cranking. OVERCRANK
  Fix: A. Check for empty fuel tank(LPG Vapor), fuel or leaks, or plugged fuel lines and correct as required.
• OVERCRANK lamp lights and engine stops cranking
  Cause: Possible fuel system problem
  Fix: Check for empty fuel tank (LPG Vapor), fuel or leaks, or plugged fuel lines and correct as required; check for dirty fuel filter (if installed) and replace if necessary; check for dirty or plugged air filter and replace if necessary (see Maintenance section); 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
  Fix: Reset breaker; contact an authorized service center if voltage buildup causes breaker to trip
• LO OIL PRES lamp lights. Engine shuts down. LO OIL PRES
  Fix: NOTE: See also step 5. a. 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 lamp lights. Engine continues to run....or LO FUEL lamp lights. Engine shuts down and LO OIL PRES lamp lights
  Cause: Interruption of natural gas supply
  Fix: Install the fuel hose and regulator supplied with the unit and connect to a propane fuel supply. Move the selector switch below control panel to the PROPANE position
• LO FUEL (Pressure) lamp lights. Shutdown will occur if unit runs out of fuel. LO FUEL (Pressure)
  Fix: Install the fuel hose and regulator supplied with the unit and connect to a propane fu
• LO FUEL (Pressure) lamp lights. Shutdown will occur if unit runs out of fuel
  Cause: Interruption of natural gas supply
  Fix: Install the fuel hose and regulator supplied with the unit and connect to a propane fuel supply; move the selector switch on governor bracket to the PROPANE position

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

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.