Cummins/Onan Quiet Diesel 12500 troubleshooting: 8 fault codes and symptom-cause-remedy entries from the manufacturer's own service documentation.
Cummins/Onan Quiet Diesel 12500 — full specs, parts & maintenance.
All Cummins/Onan fault codes →
| Symptom | Cause | Remedy |
|---|---|---|
| FAILS TO CRANK | 1. Low battery. 2. Bad battery connection. 3. Blown fuse. | 1. Check battery fluid level. 2. Clean & tighten all battery & cable connections. 3. Replace fuse on control panel. |
| CRANKS SLOWLY | 1. Low battery. 2. Bad battery connection. 3. Incorrect oil viscosity. 4. Load connected. | 1. Check battery fluid level. 2. Clean & tighten all battery & cable connections. 3. Replace with recommended viscosity oil. 4. Disconnect load before starting. |
| CRANKS BUT WON’T START | 1. Fuel below generator pickup level in tank. 2. Fuel supply shutoff valve closed. 3. Carbon deposits on spark plug(s). 4. Low oil level. | 1. Add fuel. 2. Fully open fuel supply valve. 3. Remove spark plug(s) and replace. 4. Add oil. |
| EXHAUSTING BLACK SMOKE | 1. Dirty air filter. | Replace air filter. |
| UNIT RUNS THEN STOPS, OR STOPS WHEN DRIVING AROUND A CORNER | 1. Low fuel level. 2. Low oil level. 3. Excess oil. | 1. Add fuel. 2. Add oil. 3. Reduce engine oil level. |
| UNIT STARTS AND RUNS, THEN STOPS WHEN THE START SWITCH IS RELEASED | 1. Low fluid levels. | Check & bring all fluids up to the appropriate levels. |
| UNIT RUNS THEN SURGES | 1. Loose or worn spark plug leads. 2. Defective ignition coil, wiring, or control components. 3. Faulty spark plug. 4. Governor out of adjustment. 5. Combustion air pre-heat malfunction. 6. Carburetor icing. 7. Carburetor varnishing. | 1. Check spark plug leads at spark plug & ignition coil. 2. Contact an Onan Authorized RV Service & Parts Dealer. 3. Remove spark plug & clean or replace. 4. Contact an Onan Authorized RV Service & Parts Dealer. 5. Contact an Onan Authorized RV Service & Parts Dealer. 6. Move carburetor pre-heater to the winter position. 7. Try fuel system cleaner and contact dealer if no change. |
| CIRCUIT BREAKER TRIPS | 1. Overloaded circuit. | Turn-off some of the electrical load, and reset the circuit breaker. |
Fault codes and symptom→remedy steps extracted from this model’s service/owner documentation; verify against the official manual before servicing.
Documented causes: 1. Low battery. 2. Bad battery connection. 3. Blown fuse.. See the table for the matching fixes.
Documented causes: 1. Low battery. 2. Bad battery connection. 3. Incorrect oil viscosity. 4. Load connected.. See the table for the matching fixes.
Documented causes: 1. Fuel below generator pickup level in tank. 2. Fuel supply shutoff valve closed. 3. Carbon deposits on spark plug(s). 4. Low oil level.. See the table for the matching fixes.