Cummins/Onan LRG-423 (Turbocharged) Engine

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

• Engine will not crank 12
  Cause: Indicates possible fault with control or starting system; fault lamp on
  Fix: Correct fault and reset control
• PRE HET/LOP lamp lights. Engine continues to operate 2
  Cause: Indicates 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 cooling air inlets and outlets and remove any obstructions to airflow
• No AC output voltage
  Cause: Field breaker is tripped
  Fix: Reset breaker; contact an authorized service center if voltage buildup causes breaker to trip
• 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 — possible fault with control or starting system
  Cause: Fault lamp on
  Fix: Correct fault and reset control
• The OVERLOAD lamp lights. Engine shuts down 9
  Cause: The line circuit breaker is located in the ATS or generator set output box; if 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
• SWITCH OFF lamp flashes 7
  Cause: Indicates 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
• OVERCRANK lamp lights and engine stops cranking; or engine runs, shuts down, and LO OIL PRES lamp lights 5
  Cause: Indicates 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 installed on fuel line); 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
• LO OIL PRES lamp lights. Engine shuts down 4
  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 8
  Cause: Indicates interruption of natural gas supply
  Fix: Connect to a propane fuel supply (if not already connected); move the selector switch on the governor mounting bracket to the PROPANE position
• HI ENG TEMP lamp lights. Engine shuts down 3
  Cause: Indicates engine has overheated (engine temperature has risen above 215°F/102°C) or coolant level is low
  Fix: Allow engine to cool down completely before proceeding with the following checks: check coolant level and replenish if low, look for possible coolant leakage points and repair if necessary; check for obstructions to cooling airflow and correct as necessary; check for a slipping fan belt and tighten if loose; reset control and restart after locating and correcting problem; contact an authorized service center if none of the above
• Green RUN lamp lights following engine startup 1
  Cause: Indicates all engine systems are normal
  Fix: No corrective action required
• Green RUN lamp does not light following engine startup 14
  Cause: Indicates possible Start/Disconnect relay failure
  Fix: Test light with LAMP TEST position on switch; contact an authorized service center
• Engine runs and then shuts down, OVERSPEED lamp lights 6
  Cause: Indicates engine has exceeded normal operating speed
  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.

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.