Cummins/Onan EF series troubleshooting: 38 fault codes and symptom-cause-remedy entries from the manufacturer's own service documentation.
Cummins/Onan EF series — full specs, parts & maintenance.
All Cummins/Onan fault codes →
| Symptom | Cause | Remedy |
|---|---|---|
| Engine lacks power. | Tighten cylinder head and spark plugs. If still not corrected; grift the valve clearance. Replace pistons rings, if necessary. | |
| Excessive choking. | See that choke opens properly. | |
| Carbon or lead in cylinder. | Remove carbon. | |
| Restricted air cleaner. | Clean or increase the size. | |
| Engine misfires at light load. | Carburetor needs adjustment. Adjust, clean if needed. Sparkplug gaps too narrow. Adjust to correct gap. Intake air leak. Tighten or replace gaskets. Faulty ignition. Clean, adjust, or replace breaker points, plugs; condenser, coil, etc., or retime ignition. | |
| Uneven compression. | Tighten cylinder head and spark plugs. If still not corrected, grind valves. Replace piston rings, if necessary. Worn intake valve stems or guides. Replace valves or guides. | |
| Engine misfires at heavy load. | Spark plugs defective. Replace. Faulty ignition. Clean, adjust, or replace breaker points, plugs, condensers, coil, etc., or retime ignition. Clogged carburetor. Clean jets. Clogged fuel screen. Clean. | |
| Engine misfires at all loads. | Fouled spark plugs. Defective or wrong spark plug. Sticking valves. Broken valve spring. Defective ignition wires. Defective or improperly adjusted points. Defective ignition condenser. Improper valve lash. Clean and adjust. Replace. Clean stems and guides. Replace. Adjust or replace breaker points. Replace. Adjust. | |
| Low oil pressure. | Oil too light. Oil badly diluted. Oil too low. Oil relief valve not seating. Badly worn engine bearings. Drain, refill with proper oil. Drain, refill with proper oil. Add oil. Remove and clean, or replace. | |
| Plant starts but does not continue to run. | Start button released too soon. Hold in contact longer. Repair. Defective panel equipment. See Controls. | |
| Engine backfires at carburetor. | Lean fuel mixture. Glogged fuel screen. Intake air leak. Poor fuel. Spark too late. Spark plug wires crossed. Intake valves leaking. Clean or adjust carburetor. Clean screen. Replace flange gaskets, tighten carburetor. Refill with good, fresh fuel. Retime ignition. Install wires correctly. | |
| Excessive oil consumption, light blue smoky exhaust. | Sludged rings, excessive bearing clearances, piston skirt collapsed, worn intake-valve guides. Replace worn parts. Oilleaks from engine or connections. This does not cause smoky exhaust. Tighten screws and connections. | |
| Black, smoky exhaust, excessive fuel consumption, fouling of spark plugs with black soot, possible lack of power under heavy load. | Fuel mixture too rich. Be sure all jet gaskets are in place and tight; and float needle valve gas kens in place and tight. Adjust choke. Install needed carburetor parts, adjust float level. Choke not open. See that choke opens properly. Dirty carburetor air cleaner. Clean, refill to proper level. | |
| Light pounding knock. | Loose connecting rod bearing. Replace. Low oil supply. Add oil. Low oil pressure. Refer to symptom of low oil pressure for remedies. Oil badly diluted. Change oil. | |
| Engine stops unexpectedly. | Fuel tank empty. Refill. Fuel pump failure. Repair or replace. High water temperature. See symptoms for engine overheating; Defective ignition. Check the ignition system. Repair or replace parts necessary. | |
| Dull metallic thud, if not bad, may disappear after few minutes operation. If bad, increases with load. | Loose crankshaft. Replace bearings, unless one of the next three remedies permanently corrects the trouble. | |
| Sharp metallic thud, especially when cold engine first started. | Low oil supply. Add oil. Low oil pressure. Refer to symptom of low pressure for remedies. Oil badly diluted. Change oil. | |
| Pinging sound when engine is rapidly accelerated or heavily loaded. | Carbon in cylinders. Remove carbon. Spark too early. Retime ignition. Wrong spark plugs. Install correct plugs. Spark plugs burned or carboned. Install new plugs. | |
| The voltage regu""lator is in operation, but voltage is steady when regulated by the field rheostat | Adjust the regulator dash pot screw | |
| Too heavy oil in crankcase. | Drain, refill with light oil. | |
| Engine stuck. | Disassemble and repair. | |
| Defective cable. | Install new cable. | |
| ENGINE WILL NOT START WHEN CRANKED | Faulty ignition. | Clean, adjust, or replace breaker points, plugs, condenser, coil, etc.., retime ignition. |
| Lack of· fuel or faulty carburetion. | Refill the tailk, check the fuel system. Clean, adjust, or replace parts necessary. | |
| Clogged fuel screen. | Clean. | |
| Cylinders flooded. | Crank few times with spark plugs removed. | |
| Poor fuel. | Drain, refill with good fuel. | |
| Poor compression. | Tighten cylinder head and spark plugs. If still not corrected, grind the valves. Replace piston rings, if necessary. | |
| WroIlg timing. | Retime ignition. | |
| Poor chok~ng. | If plant is cold, adjust choke. If plant is warm, pull up on choke arm momentarily, while cranking. | |
| ENGINE RUNS BUT CURRENT DOES NOT BUILDUP | Poor brush contact or dirty slip rings. | See that brushes seat well, are free in holders, are not worn too short, and have good spring tension. Open circuit, short circuit or ground in generator. See GENERATOR, replace parts necessary. |
| CURRENT UNSTEADY BUT ENGINE NOT MISFIRING | Speed too low. | Adjust governor to correct speed. Poor brush contact. See that brushes seat well on slip rings, are free in holders, are not worn too short, and have good spring tension. Loose connections. Tighten connections. Fluctuating load. Correct any abnormal load condition causing trouble. |
| TAPPING SOUND | Tappet clearance too great. | Adjust or replace tappets. Broken.valvespring. Install new spring. |
| LOWO WLLING CLICKING BOUND WITH -COOL ENGINE UNDER LOAD | Loosepisrons. | If noise orily slight and disappears when engine warms up, no immediate attention needed. Otherwise replace worn parts. |
| VOLTAGE LOW AT FAR END OF LINE BUT NORMAL NEAR POWER UNIT | Too small line wire for load. | Install larger or extra wires or reduce and distance. Voltage low at far end of line but normal near power unit. |
| MOTORS RUN TOO SLOWLY AND OVERHEAT AT FAR END OF LINE BUT OK NEAR POWER UNIT | Too sman line wire for load. | Install larger or extra wires, or reduce and distance. Motors run too slowly and overheat at far end of line but ok near power unit. |
| ENGINE OVERHEATING | Low water in radiator. Overloaded. Improper lubrication. Radiator obstructed. Ignition timing late. Improper ventilation. | RefUl radiator. Remove part of load. See Low Oil Pressure. Clean radiator. Adjust ignition timing. Provide for better air change. |
| STARTER WILL NOT CRANK ENGINE | Discharged battery. Corroded terminals. Loose connections. Defective starter relay. | Test and recharge or replace battery. Clean and tighten terminals. Tighten connections. Clean.contacts if necessary. Replace switch if necessary. |
Fault codes and symptom→remedy steps extracted from this model’s service/owner documentation; verify against the official manual before servicing.
Documented causes: Faulty ignition.. See the table for the matching fixes.
Documented causes: Poor brush contact or dirty slip rings.. See the table for the matching fixes.
Documented causes: Speed too low.. See the table for the matching fixes.