Cummins/Onan battery charging plants troubleshooting: 26 fault codes and symptom-cause-remedy entries from the manufacturer's own service documentation.
Cummins/Onan battery charging plants — full specs, parts & maintenance.
All Cummins/Onan fault codes →
| Symptom | Cause | Remedy |
|---|---|---|
| ENGINE CRANKS TOO STIFFLY | Too heavy oil in crankcase, Drain. Refill-with lighter oil. See PREPARATION. | Drain. Refill-with lighter oil. Disassemble and repair. |
| ENGINE CRANKS. TOO SLOWLY WHEN CRANKED ELECTRICALLY | Discharged or defective battery, Loose connections, Corroded battery terminals. | Recharge or replace. Tighten loose connections. Clean corroded terminals. Replace cable if necessary. |
| ENGINE WILL NOT START WHEN CRANKED | Faulty ignition, Lack of fuel or faulty carburetion, Clogged fuel filter, Cylinders flooded, Poor fuel. | Clean, adjust, or replace breaker points, spark plugs, condenser, etc., or retime ignition. Refill the tank. Check the fuel system. Clean. |
| ENGINE RUNS BUT VOLTAGE DOES NOT BUILD UP | Poor brush contact, Open circuit, short circuit, or ground in generator. | See that brushes seat well on commutator and collector rings, are free in holders, are not worn shorter than 5/8 inch, and have good spring tension. Refer to the GENERATOR section-of MAINTENANCE and REPAIR. |
| VOLTAGE UNSTEADY BUT ENGINE NOT MISFIRING | Speed too low, Poor commutation or brush contact. | Adjust governor to correct speed. Refinish commutator or undercut mica if necessary. See that brushes seat well on commutator and collector rings; are free in holders, are not worn shorter than 5/8 inch, and have good spring tension. |
| ENGINE OVERHEATING | Short in load circuit, Generator overloaded, Improper brush rig position. | Correct short circuit. Reduce the load. See BRUSHES, MAINTENANCE and REPAIR. |
| VOLTAGE DROPS UNDER HEAVY LOAD | Engine lacks power, Poor compression, Faulty carburetion, Dirty carburetor air cleaner, Choke, Carbon in cylinders or in carburetor venturi, Restricted exhaust line. | See remedies under 'ENGINE MISFIRES AT HEAVY LOAD'. Tighten cylinder heads and spark plugs. If still not corrected, grind the valves. Replace piston rings if necessary. Clean, adjust, or repair as needed. Clean. Refill with proper oil. Choke plate must be wide open at operating temperature. Clean. Remove carbon. Clean or increase the size. |
| ENGINE MISFIRES AT LIGHT LOAD | Carburetor, idle jet clogged or improperly adjusted, Spark plug gaps too narrow, Intake air leak. | Clean. Adjust to correct gap. Tighten manifold and carburetor mounting screws. Replace gaskets if necessary. |
| ENGINE MISFIRES AT ALL LOADS | Fouled spark plug, Defective or wrong spark plug, Leaking valves, Broken valve spring, Defective or improperly adjusted breaker points. | Replace. Clean, adjust, or replace breaker points, spark plugs, condenser, etc., or retime ignition. |
| LOW OIL PRESSURE | Oil too light, Oil badly diluted, Oil too low, Oil relief valve not seating, Badly worn bearings, Sludge on oil screen, Badly worn oil pump, Defective oil pressure gauge. | Drain, refill with proper oil. Drain, refill with proper oil. Add oil. Remove and clean or replace: Replace. Remove and clean. Replace. Replace. |
| HIGH OIL PRESSURE | Oil too heavy. Clogged oil passage. Oil relief valve stuck. | Drain, refill -with proper oil. Clean all lines and passages. Remove and clean. |
| ENGINE BACKFIRES AT CARBURETOR | Lean fuel mixture. Clogged fuel filter. Air leak at intake manifold or carburetor flange. | Clean carburetor, Adjust jets. Clean. Tighten mounting screws. Replace gaskets if necessary. |
| EXCESSIVE OIL CONSUMPTION, LIGHT BLUE SMOKY EXHAUST | Poor compression. Due to worn pistons, rings, or cylinders. | Refinish cylinders. Install oversize pistons and rings. |
| ENGINE MISFIRES AT ALL SPEEDS | Refer to 'ENGINE MISFIRES AT ALL SPEEDS'. | |
| BLACK, SMOKY EXHAUST, EXCESSIVE FUEL CONSUMPTION, FOULING OF SPARK PLUGS WITH BLACK SOOT, POSSIBLE LACK OF POWER UNDER HEAVY LOAD | Fuel mixture too rich. Choke not fully open. Dirty air cleaner. | See that choke opens properly. Adjust jets properly. Clean, refill with proper oil. |
| LIGHT POUNDING KNOCK | Loose connecting rod. | Adjust clearance or replace. |
| ENGINE STOPS UNEXPECTEDLY | Empty fuel tank. Defective ignition system. Defective STOP button lead is grounded. | Refill. Check the ignition system. Repair or replace as needed. See that the STOP button lead is not grounded. |
| DULL METALLIC THUD, IF NOT BAD, MAY DISAPPEAR AFTER FEW MINUTES OF OPERATION, IF BAD, INCREASES WITH LOAD | Loose crankshaft bearing. | Replace, unless one of the next two remedies permanently corrects the trouble. |
| SHARP METALLIC THUD, ESPECIALLY WHEN COLD ENGINE FIRST STARTED | Low oil supply. Oil badly diluted. | Add oil. Change if necessary. Drain, refill with proper oil. |
| PINGING SOUND WHEN ENGINE IS SUDDENLY OR HEAVILY LOADED | Carbon in cylinders. Spark advanced too far. Wrong spark plugs. | Remove the carbon. Reset breaker points or retime ignition. Install correct spark plugs, Champion H9 Com. Clean. Install new plugs if necessary. |
| TAPPING SOUND | Valve clearance too great. | Adjust to proper clearance. See VALVE SERVICE. Install new spring. |
| HOLLOW CLICKING SOUND WITH COOL ENGINE UNDER LOAD | Loose piston: If noise is only slight and disappears when engine warms up, no immediate attention needed. | Otherwise replace parts necessary. |
| VOLTAGE LOW AT FAR END OF LINE BUT NORMAL NEAR PLANT | Too small line wire used for load and distance. | Install larger or extra wires or reduce load. |
| MOTORS RUN TOO SLOWLY AND OVERHEAT AT FAR END OF LINE BUT OK NEAR PLANT | Too small line wire used for load and distance. | Install larger or extra wires or reduce load. |
| NOISY BRUSHES | High mica between bars of commutator. | Undercut mica. |
| EXCESSIVE ARCING OF BRUSHES | Rough commutator or rings. Dirty commutator or rings. Brushes not seating properly. | Turn down. Clean. Sand to a good seat or re until worn in. |
Fault codes and symptom→remedy steps extracted from this model’s service/owner documentation; verify against the official manual before servicing.
Documented causes: Too heavy oil in crankcase, Drain. Refill-with lighter oil. See PREPARATION.. See the table for the matching fixes.
Documented causes: Discharged or defective battery, Loose connections, Corroded battery terminals.. See the table for the matching fixes.
Documented causes: Faulty ignition, Lack of fuel or faulty carburetion, Clogged fuel filter, Cylinders flooded, Poor fuel.. See the table for the matching fixes.