Cummins/Onan 4.0 BF troubleshooting: 25 fault codes and symptom-cause-remedy entries from the manufacturer's own service documentation.
Cummins/Onan 4.0 BF — full specs, parts & maintenance.
All Cummins/Onan fault codes →
| Symptom | Cause | Remedy |
|---|---|---|
| Bad Battery Connection | BT I | |
| Low Battery | BT I | |
| Wrong Spark | Check ignition system | |
| Out of Fuel Check | Check fuel system | |
| Engine Flooded | Drain excess fuel | |
| Poor Qual ty Fuel | Use high quality fuel | |
| Dirty Carburetor | Clean carburetor | |
| Dirty A Cleaner | Clean air cleaner | |
| Dirty Fuel Filter | Replace fuel filter | |
| Defec ive Fuel Pump | Replace fuel pump | |
| Piston Rings | Worn or broken | Replace piston rings |
| Wrong Bearin g | Replace bearing | |
| Broken Valve S in | Replace valve | |
| Defective Oil Gauge | Calibrate or replace oil gauge | |
| Retie Valve Stuck | Lubricate valve | |
| Faulty 0 I Pump | Replace oil pump | |
| Dirty Oil or Filter | Change oil and filter | |
| Oil Le el Low | Add more oil | |
| Oil Too Heavy | Change to lighter weight oil | |
| Dirty Crankcase Breather Val e | Clean breather valve | |
| Linkage Binding | Lubricate or adjust linkage | |
| Fuel leaks from carburetor. | Float level set too high; Dirt under inlet valve; Bowl vent plugged; Collapsed float caused by blowing assembled carburetor with compressed air; Carburetor gummed from storage. Float stuck to screen | With fuel bowl removed and carburetor inverted, set float parallel to bowl flange (3/32" clearance); Remove inlet valve, clean seat by rinsing in clean fuel and blow off with compressed air; Remove bowl and blow clean with compressed air; Replace float; Remove fuel bowl and clean with suitable solvent |
| Engine smokes and runs rich. | Dirty air filter; Improper adjustment; Nozzle boss gasket leaks. Engine runs with power needle seated; Air bleeds in carburetor plugged | Clean or replace; Set idle and power needles at one turn open. After engine starts and runs, set for optimum performance; Remove fuel bowl and replace gasket. Tighten bowl retainer securely; Remove fuel bowl, idle and power needles. Clean thoroughly with compressed air |
| Engine runs lean. | Improper adjustment; Idle holes plugged; Float level set too low. Low level in fuel bowl | Set idle and power needles at one turn open. After engine starts and runs, set for optimum performance; Remove fuel bowl, idle and power needles. Clean thoroughly with compressed air; With fuel bowl removed and carburetor inverted, set float parallel to bowl flange (3/32" clearance) |
| Engine starts hard. | Improper adjustment; No fuel in carburetor; Ch | Set idle and power needles at one turn open. After engine starts and runs, set for optimum performance; Check carburetor drain valve. If no fuel in bowl, clean tank filter and carburetor. Check electric fuel pump operation. Check electric solenoid valve |
Fault codes and symptom→remedy steps extracted from this model’s service/owner documentation; verify against the official manual before servicing.
Documented causes: BT I. See the table for the matching fixes.
Documented causes: BT I. See the table for the matching fixes.
Documented causes: Worn or broken. See the table for the matching fixes.