Cummins/Onan battery charging plants troubleshooting: 105 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. |
| Engine cranks too stiffly | Engine stuck | Disassemble and repair. |
| Engine cranks too slowly when cranked electrically | Discharged or defective battery | Recharge or replace. |
| Engine cranks too slowly when cranked electrically | Loose connections | Tighten loose connections. |
| Engine cranks too slowly when cranked electrically | Corroded battery terminals | Clean corroded terminals. Replace cable if necessary. |
| Engine cranks too slowly when cranked electrically | Brushes worn excessively or making poor contact | Replace brushes or clean commutator. |
| Engine cranks too slowly when cranked electrically | Short circuit in generator or load circuit | Repair or replace parts necessary. Disconnect load. |
| Engine cranks too slowly when cranked electrically | Dirty or corroded points in start solenoid switch | Replace switch. |
| Engine will not start when cranked | Faulty ignition | Clean, adjust, or replace breaker points, spark plugs, condenser, etc., or retime ignition. |
| Engine will not start when cranked | Lack of fuel or faulty carburetion | Refill the tank. Check the fuel system. Clean, adjust, or replace parts necessary. |
| Engine will not start when cranked | Clogged fuel filter | Clean. |
| Engine will not start when cranked | Cylinders flooded | Ground spark plug cables. Crank engine with spark plugs removed. |
| Engine will not start when cranked | Poor fuel | Drain. Refill with good fuel. |
| Engine will not start when cranked | Poor compression | Tighten cylinder heads and spark plugs. If still not corrected, grind the valves. Replace piston rings if necessary. |
| Engine will not start when cranked | Wrong ignition timing | Reset breaker points or retime ignition. See IGNITION. |
| Engine runs but voltage does not build up | Poor brush contact | 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 runs but voltage does not build up | Open circuit, short circuit, or ground in generator | Refer to the GENERATOR section of MAINTENANCE and REPAIR. |
| Voltage unsteady but engine not misfiring | Speed too low | Adjust governor to correct speed. |
| Voltage unsteady but engine not misfiring | Poor commutation or brush contact | 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. |
| Voltage unsteady but engine not misfiring | Loose connections | Tighten connections. |
| Voltage unsteady but engine not misfiring | Fluctuating load | Correct any abnormal load condition causing trouble. |
| Generator overheating | Short in load circuit | Correct short circuit. |
| Generator overheating | Generator overloaded | Reduce the load. |
| Generator overheating | Improper brush rig position | See BRUSHES, MAINTENANCE and REPAIR. |
| Engine overheating | Improper lubrication | See Low Oil Pressure. |
| Engine overheating | Poor ventilation | Provide ample ventilation at all times. |
| Engine overheating | Dirty or oily cooling surfaces | Keep the engine clean. |
| Engine overheating | Retarded ignition timing | Retime ignition. |
| Engine overheating | Generator overloaded | Reduce load. |
| Voltage drops under heavy load | Engine lacks power | See remedies under "ENGINE MISFIRES AT HEAVY LOAD". |
| Voltage drops under heavy load | Poor compression | Tighten cylinder heads and spark plugs. If still not corrected, grind the valves. Replace piston rings if necessary. |
| Voltage drops under heavy load | Faulty carburetion | Check the fuel system. Clean, adjust, or repair as needed. |
| Voltage drops under heavy load | Dirty carburetor air cleaner | Clean. Refill with proper oil. |
| Voltage drops under heavy load | Choke | Choke plate must be wide open at operating temperature. |
| Voltage drops under heavy load | Carbon in cylinders or in carburetor venturi | Remove carbon. |
| Voltage drops under heavy load | Restricted exhaust line | Clean or increase the size. |
| Engine misfires at light load | Carburetor idle jet clogged or improperly adjusted | Clean. |
| Engine misfires at light load | Spark plug gaps too narrow | Adjust to correct gap. |
| Engine misfires at light load | Intake air leak | Tighten manifold and carburetor mounting screws. Replace gaskets if necessary. |
| Engine misfires at light load | Faulty ignition | Clean, adjust, or replace breaker points, spark plugs, condenser, etc. |
| Engine misfires at light load | Poor compression | Tighten cylinder heads and spark plugs. If still not corrected, grind the valves. Replace piston rings if necessary. |
| Engine misfires at heavy load | Defective spark plug | Replace. |
| Engine misfires at heavy load | Faulty ignition | Clean, adjust, or replace breaker points, spark plugs, condenser, etc., or retime ignition. |
| Engine misfires at heavy load | Clogged carburetor | Clean carburetor. |
| Engine misfires at heavy load | Clogged fuel screen | Clean. |
| Engine misfires at heavy load | Defective spark plug cable | Replace. |
| Engine misfires at all loads | Fouled spark plug | Clean and adjust. |
| Engine misfires at all loads | Defective or wrong spark plug | Replace. |
| Engine misfires at all loads | Leaking valves | See VALVE SERVICE. |
| Engine misfires at all loads | Broken valve spring | Replace. |
| Engine misfires at all loads | Defective or improperly adjusted breaker points | Adjust or replace breaker points. |
| Low oil pressure | Oil too light | Drain, refill with proper oil. |
| Low oil pressure | Oil badly diluted | Drain, refill with proper oil. |
| Low oil pressure | Oil too low | Add oil. |
| Low oil pressure | Oil relief valve not seating | Remove and clean, or replace. |
| Low oil pressure | Badly worn bearings | Replace. |
| Low oil pressure | Sludge on oil screen | Remove and clean. |
| Low oil pressure | Badly worn oil pump | Replace. |
| Low oil pressure | Defective oil pressure gauge | Replace. |
| High oil pressure | Oil too heavy | Drain, refill with proper oil. |
| High oil pressure | Clogged oil passage | Clean all lines and passages. |
| High oil pressure | Oil relief valve stuck | Remove and clean. |
| High oil pressure | Defective oil pressure gauge | Replace. |
| Engine backfires at carburetor | Lean fuel mixture | Clean carburetor. Adjust jets. |
| Engine backfires at carburetor | Clogged fuel filter | Clean. |
| Engine backfires at carburetor | Air leak at intake manifold or carburetor flange | Tighten mounting screws. Replace gaskets if necessary. |
| Engine backfires at carburetor | Poor fuel | Refill with good, fresh fuel. See PREPARATION. |
| Engine backfires at carburetor | Spark advanced too far | Reset breaker points or retime ignition. |
| Engine backfires at carburetor | Intake valve leaking | Reseat or replace. |
| Excessive oil consumption, light blue smoky exhaust | Poor compression, usually due to worn pistons, rings, or cylinders | Refinish cylinders. Install oversize pistons and rings. |
| Excessive oil consumption, light blue smoky exhaust | Oil too light or diluted | Drain, refill with proper oil. |
| Excessive oil consumption, light blue smoky exhaust | Too large bearing clearance | Replace bearings if necessary. |
| Excessive oil consumption, light blue smoky exhaust | Engine misfires | Refer to "ENGINE MISFIRES AT ALL SPEEDS". |
| Excessive oil consumption, light blue smoky exhaust | Faulty ignition | Clean, adjust, or replace breaker points, spark plugs, condenser, etc., or retime the ignition. |
| Excessive oil consumption, light blue smoky exhaust | Too much oil | Drain excess oil. |
| Black, smoky exhaust, excessive fuel consumption, fouling of spark plugs with black soot, possible lack of power under heavy load | Fuel mixture too rich | See that choke opens properly. Adjust jets properly. Adjust the float level. |
| Black, smoky exhaust, excessive fuel consumption, fouling of spark plugs with black soot, possible lack of power under heavy load | Choke not fully open | See that choke opens properly. |
| Black, smoky exhaust, excessive fuel consumption, fouling of spark plugs with black soot, possible lack of power under heavy load | Dirty air cleaner | Clean, refill with proper oil. |
| Light pounding knock | Loose connecting rod | Adjust clearance or replace. |
| Light pounding knock | Low oil supply | Add oil. Change if necessary. |
| Light pounding knock | Oil badly diluted | Drain, refill with proper oil. |
| Light pounding knock | Low oil pressure | See LOW PRESSURE for remedies. |
| Engine stops unexpectedly | Empty fuel tank | Refill. |
| Engine stops unexpectedly | Defective ignition system | 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 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 | Add oil. Change if necessary. |
| Sharp metallic thud, especially when cold engine first started | Oil badly diluted | Drain, refill with proper oil. |
| Pinging sound when engine is suddenly or heavily loaded | Carbon in cylinders | Remove the carbon. |
| Pinging sound when engine is suddenly or heavily loaded | Spark advanced too far | Reset breaker points or retime ignition. |
| Pinging sound when engine is suddenly or heavily loaded | Wrong spark plugs | Install correct spark plugs. Champion H9 Com. |
| Pinging sound when engine is suddenly or heavily loaded | Spark plugs burned or carboned | Clean. Install new plugs if necessary. |
| Pinging sound when engine is suddenly or heavily loaded | Valves hot | Adjust tappet clearance. See VALVE SERVICE. |
| Pinging sound when engine is suddenly or heavily loaded | Fuel stale or low octane | Use good, fresh fuel. See PREPARATION. |
| Pinging sound when engine is suddenly or heavily loaded | Lean fuel mixture | Clean fuel system. Adjust carburetor jets properly. |
| Tapping sound | Valve clearance too great | Adjust to proper clearance. See VALVE SERVICE. |
| Tapping sound | Broken valve spring | 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 | Turn down. |
| Excessive arcing of brushes | Dirty commutator or rings | Clean. |
| Excessive arcing of brushes | Brushes not seating properly | Sand to a good seat or re[place] until worn in. |
| Excessive arcing of brushes | Open circuit in armature | Install a new armature. |
| Excessive arcing of brushes | Brush rig out of position | Line up properly. |
Fault codes and symptom→remedy steps extracted from this model’s service/owner documentation; verify against the official manual before servicing.
Documented causes: Oil too light; Oil badly diluted; Oil too low; Oil relief valve not seating. See the table for the matching fixes.
Documented causes: Faulty ignition; Lack of fuel or faulty carburetion; Clogged fuel filter; Cylinders flooded. See the table for the matching fixes.
Documented causes: Engine lacks power; Poor compression; Faulty carburetion; Dirty carburetor air cleaner. See the table for the matching fixes.