Cummins/Onan P4500 troubleshooting: 12 fault codes and symptom-cause-remedy entries from the manufacturer's own service documentation.
Cummins/Onan P4500 — full specs, parts & maintenance.
All Cummins/Onan fault codes →
| Symptom | Cause | Remedy |
|---|---|---|
| ENGINE DOES NOT CRANK (ELECTRIC START) | Bad battery connection | Clean and tighten battery connections |
| ENGINE CRANKS SLOWLY (ELECTRIC START) | Load is connected | Disconnect load while starting |
| Fouled spark plug | Remove and clean or replace spark plug | |
| ENGINE WON'T START | Low oil level | Add oil as necessary |
| BLACK EXHAUST | Contact an Onan service center | |
| ENGINE STOPS | Low oil level | Add oil as necessary |
| Generator set not level | Move generator set to level surface | |
| ENGINE SURGES | Dirty fuel strainer | Have the strainer cleaned |
| NO AC OUTPUT | Tripped AC circuit breaker | Remove all loads, reset breaker, check loads for defects. Do not exceed generator set rating. |
| NO DC OUTPUT | Tripped DC circuit breaker | Disconnect battery, reset breaker and have battery tested for shorts |
| Engine is running, but no electrical output. | 1. Reset breaker is tripped. 2. The power cord’s plug connector is not fully engaged in the inverter’s outlet. 3. Faulty or defective power cord 4. Faulty or defective electrical appliance | 1. Reset the reset breaker. 2. Verify plug connector is firmly engaged in the inverter’s outlet. 3. Replace power cord. 4. Try connecting a known good appliance to verify the inverter is producing electrical power. |
| Engine will not start or remain running while trying to start. | 1. Inverter is out of gasoline. 2. Fuel flow is obstructed. 3. Dirty air filter 4. Low oil level shutdown switch is preventing the unit from starting. 5. Spark plug boot is not fully engaged with the spark plug tip. 6. Spark plug is faulty. 7. Dirty/plugged spark arrestor 8. Stale fuel | 1. Add gasoline to the inverter. 2. Inspect and clean fuel delivery passages. 3. Check and clean the air filter. 4. Check oil level and add oil if necessary. 5. Firmly push down on the spark plug boot to ensure the boot is fully engaged. 6. Remove and check the spark plug. Replace if faulty. 7. Check and clean the spark arrestor. 8. Drain any remaining fuel from the float bowl. |
Fault codes and symptom→remedy steps extracted from this model’s service/owner documentation; verify against the official manual before servicing.
Documented causes: Bad battery connection. See the table for the matching fixes.
Documented causes: Load is connected. See the table for the matching fixes.
Documented causes: Low oil level. See the table for the matching fixes.