Cummins/Onan G8.3 Series troubleshooting: 8 fault codes and symptom-cause-remedy entries from the manufacturer's own service documentation.
Cummins/Onan G8.3 Series — full specs, parts & maintenance.
All Cummins/Onan fault codes →
| Symptom | Cause | Remedy |
|---|---|---|
| Coolant Loss - External | - Coolant level is above specification - External coolant leak - Radiator cap is not correct, is malfunctioning, or has low-pressure rating - Fill line or vent lines are restricted, obstructed, or not routed correctly - Coolant fill line is restricted or obstructed | Check the coolant level. Inspect the engine for coolant leaking from hoses, draincocks, water manifold, expansion and pipe plugs, fittings, radiator core, exhaust heat shield, heat exchanger, air compressor and cylinder head gaskets; lubricating oil cooler, water pump seal, and OEM-mounted components that have coolant flow. Check the radiator pressure cap. Check the vent lines and the fill line for correct routing and for restriction. Check the coolant fill line for restrictions or obstructions. |
| Coolant Temperature Above Normal - Gradual Overheat | - Coolant level is below specification - Lubricating oil level is above or below specification - Load is excessive for engine horsepower rating - Coolant temperature gauge is malfunctioning - Radiator fins are damaged or obstructed with debris - Radiator cap is not correct, is malfunctioning, or has low-pressure rating - Cooling system hose is collapsed, restricted, or leaking | Inspect the engine and cooling system for external coolant leaks. Repair if necessary. Add coolant. Check the oil level. Add or drain oil, if necessary. Reduce the load on the engine. Test the temperature gauge. Replace the gauge if necessary. Inspect the radiator fins. Clean and repair the fins as necessary. Check the radiator pressure cap. Inspect the hoses. |
| Coolant Temperature Below Normal | - Engine is operating at low ambient temperature - Temperature gauge malfunction - Thermostat is not operating properly | Check the shutters and engine compartment air. Check or replace the temperature gauge. Check the thermostat for correct operation. |
| Engine Decelerates Slowly | Electronic control module system calibration is not correct | Compare the calibration in the electronic control system with the engine rating and the Control Parts |: List (CPL), Bulletin number 3379133 or 4021327. If necessary, calibrate the system. Refer to a Cummins Authorized Repair Facility. Check the throttle plate for sticking or hysteresis. |
| Engine Runs Rough or Misfires | Engine is misfiring | |
| Engine Starts But Will Not Keep Running | Manual fuel valve closed, Load is excessive for engine horsepower rating, Air intake system restriction, Exhaust system restriction is not within specification, Fuel supply pressure is below specification, Low or no fuel pressure at the mixer (secondary pressure) | Open manual fuel valve, Reduce the load on the engine, Inspect the air intake system for restriction, Replace the air filter, Check the exhaust system for restrictions, Contact a Cummins Authorized Repair Facility, Increase output pressure from the secondary fuel it the mixer (secondary regulator) |
| Engine Vibration Excessive | Engine is misfiring | |
| Engine Will Not Crank or Cranks Slowly (Air Starter) | Starting procedure is not correct, Crankshaft rotation is impaired, Starting air pressure low, Starting circuit component is malfunctioning | Verify the correct starting procedure, Check the crankshaft for ease of rotation, Check the starting circuit component |
Fault codes and symptom→remedy steps extracted from this model’s service/owner documentation; verify against the official manual before servicing.
Documented causes: - Coolant level is above specification - External coolant leak - Radiator cap is not correct, is malfunctioning, or has low-pressure rating - Fill line or vent lines are restricted, obstructed, or not routed correctly - Coolant fill line is restricted or obstructed. See the table for the matching fixes.
Documented causes: - Coolant level is below specification - Lubricating oil level is above or below specification - Load is excessive for engine horsepower rating - Coolant temperature gauge is malfunctioning - Radiator fins are damaged or obstructed with debris - Radiator cap is not correct, is malfunctioning, or has low-pressure rating - Cooling system hose is collapsed, restricted, or leaking. See the table for the matching fixes.
Documented causes: - Engine is operating at low ambient temperature - Temperature gauge malfunction - Thermostat is not operating properly. See the table for the matching fixes.