Cummins/Onan CCK troubleshooting: 40 fault codes and symptom-cause-remedy entries from the manufacturer's own service documentation.
Cummins/Onan CCK — full specs, parts & maintenance.
All Cummins/Onan fault codes →
| Symptom | Cause | Remedy |
|---|---|---|
| The speed may remain about the same or increase when the load is applied, resulting in a frequency 1 or 2-cycles Aigker than the no load frequency. | If the rise in frequency is more than 2-cycles, lessen the internal spring tension. If there is a drop in the frequency, increase the booster internal spring tension. To increase the tension, pull out on the spring bracket, and move the pin to a different hole. | |
| Engine will not start when cranked | Battery discharged. Loose connections. Defective starting circuit. Defective switch. | Refill tank. Check fuel system. Clean, adjust, as necessary. Crank few times with spark plugs removed. Drain, refill with fresh fuel. Tighten cylinder heads & spark plugs. Reset breaker points. |
| Engine cranks too stiffly | Too heavy oil in crankcase. | Drain, refill with lighter oil. |
| Hot crank | Lack of fuel or faulty carburetion. | Tighten connections. Clogged fuel screen. Repait or replace as necessary. Cylinders flooded. Replace. Poor fuel. Poor compression. |
| Excessive oil consumption, light blue smoky exhaust | Oil leaks from oil base or connections, This does not cause smoky exhaust. | Check breather valve. |
| Engine misfiring. | Faulty ignition. | Clean, adjust, or replace spark plugs. |
| BLACK, SMOKY EXHAUST, EXCESSIVE FUEL CONSUMPTION, FOUCING OF SPARK PLUG WITH SOOT, POSSIBLE LACK OF POWER UNDER HEAVY LOAD | Fuel mixture too rich. | Adjust carburetor or choke. Install needed carburetor parts. |
| Engine stops unexpectedly. | Fuel tank empty. | Fill with fresh fuel. |
| SHARP METALLIC THUD, ESPECIALLY WHEN COLD ENGINE FIRST STARTED | Low oil supply. | Add oil. |
| Oil badly diluted. | Change oil. | |
| PINGING SOUND WHEN ENGINE IS SUDDENLY OR HEAVILY LOADED! | Wrong spark plug. | Install correct spark plug. |
| Spark plug burned or carboned. | Install new plug. | |
| Fuel stale or low octane. | Use good, fresh fuel. | |
| LEAN FUEL MIXTURE. | Clean or adjust carburetor. Clean intake air line. | |
| LIGHT POUNDING KNOCK | Inspect linkage and setting. | Clean & adjust carburetor. |
| Low air supply. | Add oil. Change oil. | |
| ENGINE MISFIRES AT LIGHT LOAD | Spark plug gap too narrow. | Adjust to correct gap. Tighten or replace manifold and carburetor gaskets. |
| INTAKE AIR LEAK. | Tighten or replace manifold and carburetor gaskets. | |
| FAULTY IGNITION. | Clean, adjust or replace spark plugs. Tighten cylinder head & spark plugs. Grind valves. | |
| LOW COMPRESSION. | Tighten cylinder head & spark plugs. Grind valves. | |
| ENGINE MISFIRES AT HEAVY LOAD | Spark plug gap too wide | Adjust gap |
| CLOGGED CARBURETOR. | Clean, adjust or replace spark plugs. Clean jet and adjust carb. | |
| CLOGGED FUEL SCREEN. | Clean, adjust or replace spark plugs. Clean jet and adjust carb. | |
| ENGINE BACKFIRES | Lean fuel mixture. | Clean or adjust carburetor. |
| ENGINE RACES | Governor not controlling carburetor. | Check governor performance & linkage condition. Refill with good, fresh fuel. |
| LOW OIL PRESSURE | Defective gage. | Replace. |
| Oil too light or diluted from leaking fuel pump diaphragm. | Drain. Refill with proper oil. Repair or replace fuel pump. | |
| Oil taa low. | Add oil. | |
| Sludge on oil cup screen. | Clean screen & air sump. | |
| Badly worn oil pump. | Replace. | |
| HIGH OIL PRESSURE | Defective gage. | Replace. |
| Oil too heavy grade. | Drain. Refill. | |
| Clogged oil passages. | Clean all lines & passages. | |
| Oil relief valve stuck. | Clean by-pass. Replace if needed. | |
| ENGINE OVERHEATING (Approximasely 60°F higher than ambient) | Overloaded. | Reduce load. |
| VOLTAGE LOW AT FAR END OF LINE BUT NORMAL NEAR POWER PLANT | Too small line wire for load and distance. | Install larger or extra wires. Or reduce load. |
| ELECTRIC MOTOR RUNS TOO SLOWLY AND OVERHEATS AT FAR END OF LINE BUT OK IF USED NEAR POWER UNIT | Too small line wire for load and distance. | Install larger or extra wires. Or reduce load. |
| VOLTAGE UNSTEADY BUT ENGINE NOT MISFIRING | Speed too low. | Adjust governor to correct speed. |
| Loose connections. | Tighten connections. | |
| Correct any abnormal load condition causing trouble. | Write a letter to the same address stating the reason for returning the part. |
Fault codes and symptom→remedy steps extracted from this model’s service/owner documentation; verify against the official manual before servicing.
Documented causes: Battery discharged. Loose connections. Defective starting circuit. Defective switch.. See the table for the matching fixes.
Documented causes: Too heavy oil in crankcase.. See the table for the matching fixes.
Documented causes: Lack of fuel or faulty carburetion.. See the table for the matching fixes.