Cummins/Onan 605MCCK troubleshooting: 41 fault codes and symptom-cause-remedy entries from the manufacturer's own service documentation.
Cummins/Onan 605MCCK — full specs, parts & maintenance.
All Cummins/Onan fault codes →
| Code | Meaning | Remedy |
|---|---|---|
| LOW OIL | Oil too light or diluted from leaking fuel pump diaphragm. | Drain, fill with proper oil. Repair or replace fuel pump. |
| LOW OIL | Oil too low. | Add oil. |
| LOW OIL | Oil relief valve not seating. | Remove. Clean all lines and passages. Replace. |
| LOW OIL | Badly worn bearings. | Replace. |
| LOW OIL | Sludge on oil screen. | Remove and clean. Replace. |
| LOW OIL | Badly worn oil pump. | Replace. |
| HIGH OIL | Oil too heavy. | Clean all lines and passages. Replace. |
| HIGH OIL | Clogged oil passage. | Remove and clean. Replace. |
| HIGH OIL | Oil relief valve stuck. | Replace. |
| Symptom | Cause | Remedy |
|---|---|---|
| Engine cranks too stiffly | Too heavy oil in crankcase. | Drain and fill with lighter oil. |
| Engine cranks too slowly when cranked electrically | Discharged or defective battery. Charge or replace.; Faulty field rectifier. Replace rectifier.; Corroded or loose battery Clean corroded terminals. Replace cable if necessary.; Brushes worn excessively Replace brushes and/or clean commutator. | |
| Engine will not start when cranked | Out of fuel. Check fuel system.; Faulty ignition. Clean, adjust, or replace breaker points, spark plugs, condenser, etc., or time ignition.; Lack of fuel or faulty carburetion. Check fuel system. Clean, adjust or replace parts as necessary.; Clogged fuel filter. Replace.; Cylinders flooded. Ground spark plug cables. Crank engine with plugs removed.; Poor fuel Drain. Fill with fresh fuel.; Poor compression. Tighten cylinder head bolts and spark plugs. If still not corrected, grind valves and/or replace piston rings.; Wrong ignition timing. Re-set breaker points or time ignition. | |
| Engine runs but voltage does not build up | Poor brush contact. Check: Brush seating on commutator and collector rings; free in holders and not worn too short and have good spring tension.; Open circuit, short circuit, Refer to the Generator section of Maintenance; Residual magnetism lost. Magnetize the field. | |
| Voltage is unsteady but engine is not misfiring | Speed too low. Adjust governor to correct speed.; 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, not worn too short, and have good spring tension.; Loose connections. Tighten.; Fluctuating load. Correct abnormal load condition causing trouble. | |
| Generator overheating | Short in load circuit. Correct short circuit.; Generator overloaded. Reduce load.; Improper brush rig position. Adjust. | |
| Engine overheating | Improper lubrication. Change to proper oil.; Provide ample ventilation at all times.; Insufficient water circulation. Clean cooling system.; Check pump and lines. | |
| Voltage drops under heavy load | Engine lacks power. See remedies under Engine Misfires at Heavy Load.; Poor compression. Tighten cylinder head bolts and spark plugs. If still not corrected, grind the valves and/or replace piston rings.; Faulty carburetion. Check fuel system. Clean, adjust or repair as needed.; Dirty flame arrester. Clean.; Choke partially closed. Choke plate must be wide open at operating temperature.; Carbon in cylinders or in carburetor venturi. Remove carbon.; Restricted exhaust line. Clean or increase size. | |
| Engine misfires at light load | Carburetor idle jet clogged or improperly adjusted. Clean.; Spark plug gaps too narrow. Set gap.; Intake air leak. Tighten. Replace gaskets if necessary.; Faulty ignition. Clean, adjust, or replace breaker points, spark plugs, condenser, etc., or time ignition. | |
| Engine misfires at heavy load | Defective spark plug. Replace.; Faulty ignition. Clean, adjust, or replace breaker points, spark plugs, condenser, etc., or time ignition.; Clogged carburetor. Clean carburetor.; Clogged fuel screen. Clean.; Defective spark plug cable. Replace. | |
| Fouled spark plug. | Clean and adjust. | |
| Defective or wrong spark plug. | Replace. | |
| Leaking valves. | Grind valves. | |
| Broken valve spring. | Replace. | |
| Defective or improperly adjusted breaker points. | Adjust or replace breaker points. | |
| Engine backfires. | Lean fuel mixture. Clogged fuel filter. Air leak at intake manifold or carburetor flange. Poor fuel. Spark advanced too far. Intake valve leaking. | |
| Excessive oil consumption, light blue exhaust. | Poor compression. Usually due to worn pistons, rings, or cylinders. Oil leaks from oil base or connections (does not cause smoky exhaust). Oil too light or diluted. Too large bearing clearance. | |
| Engine misfires. | Refinish cylinders. Install oversized pistons and rings. Replace gaskets. Tighten screws and connections. Check breather valve. Drain. Fill with proper oil. Replace bearings. Refer to Engine Misfires at All Speeds. | |
| Faulty ignition. | Clean, adjust, or replace breaker points, spark plugs, condenser, etc., or time ignition. | |
| Too much oil. | Drain excess oil. | |
| Black, smoky exhaust, excessive fuel consumption. Fouling of spark plug with black soot. | Fuel mixture too rich. See that choke opens properly. Adjust jets and float level. Choke not fully open. See that choke opens properly. Dirty flame arrester. Clean. Excessive crankcase pressure. Clean breather valve. | |
| POSSIBLE LACK OF POWER UNDER HEAVY LOAD | Fuel mixture too rich. See that choke opens properly. Adjust jets and float level. Choke not fully open. See that choke opens properly. Dirty flame arrester. Clean. Excessive crankcase pressure. Clean breather valve. | |
| Light pounding knock. | Loose connecting rod. Adjust clearance or replace. Low oil supply. Add oil. Change if necessary. Oil badly diluted. Drain. Fill with proper oil. Low oil pressure. See Low Oil Pressure for remedies. | |
| Engine stops unexpectedly. | Empty fuel tank. Fill. Defective ignition system. Check ignition system and repair or replace as needed. Engine overheating. High water temp cut out stops engine. Low oil pressure. Low oil pressure switch stops engine. | |
| Dull metallic ticking, 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. Oil badly diluted. Change oil. Carbon in cylinders. Remove the carbon. | |
| Tapping sound. | Valve clearance too great. Adjust to proper clearance. Broken valve spring. Install new spring. | |
| Hollow chinking 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. Install larger or extra wires for load and distance. or reduce load. | |
| Motors run too slowly and overheat at far end of line but OK near the plant. | Too small line wire used. Install larger or extra wires for load and distance. or reduce load. | |
| Noisy brushes. | High mica between bars of commutator. Undercut mica. | |
| Excessive arcing of brushes. | Rough commutator or rings. Turn down. Dirty commutator or rings. Clean. Brushes not seating properly. Sand to a good seat or reduce load until worn-in. Open circuit in armature. Install a new armature. 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: Too heavy oil in crankcase.. See the table for the matching fixes.