Cummins/Onan C12 D6 troubleshooting: 17 fault codes and symptom-cause-remedy entries from the manufacturer's own service documentation.
Cummins/Onan C12 D6 — full specs, parts & maintenance.
All Cummins/Onan fault codes →
| Code | Meaning |
|---|---|
| 59 | High AC voltage shutdown |
| 27 | Low AC voltage shutdown |
| 81 u | Under frequency shutdown |
| 81 o | Over frequency shutdown/warning |
| 51 | High Current warning/shutdown |
| Symptom | Cause | Remedy |
|---|---|---|
| Battery voltage warning | Status of battery charging system (failure) | |
| Emergency stop signal is received | The generator set immediately shuts down and cannot run or crank with the E-stop switch engaged. | |
| Time delay of 0-600 seconds prior to shutdown after signal to stop in normal operation modes | Default for both time delay periods is 0 seconds. | |
| Undervoltage sensor pickup and dropout adjustable from 85-100% and 75-98% | Dropout adjustable delay from 0.1-30 sec. | |
| Overvoltage sensor dropout adjustable from 105-135% of nominal | Dropout adjustable delay from 0.5-120 sec. | |
| Over/under frequency sensor underfrequency sensing pickup and dropout adjustable from 85-100% and 70-85% | Dropout adjustable delay from 0.1-15 sec. | |
| Over/under frequency sensor overfrequency sensing dropout adjustable from 105-115% of nominal | Dropout adjustable delay from 0.1-15 sec. | |
| Time delay start and stop (cooldown) configurable for time delay of 0-300 seconds prior to starting after receiving a remote start signal | Control provides retransfer time delays including time delay emergency to normal (0-1800 sec), programmed transition delay (0-600 sec), and time delay engine cooldown (0-3600 sec). | |
| Low lube oil pressure warning/shutdown | Level is pre-set to match the capabilities of the engine used. Control includes time delays to prevent nuisance shutdown signals. | |
| High coolant temperature warning/shutdown | Level is pre-set to match the capabilities of the engine used. Control includes time delays to prevent nuisance shutdown signals. | |
| Low coolant temperature warning | Indicates that engine temperature may not be high enough for 1 min. and start or proper load acceptance. | |
| Sensor failure indication | Logic is provided on the base control to detect analog sensor or interconnecting wiring failures. |
Fault codes and symptom→remedy steps extracted from this model’s service/owner documentation; verify against the official manual before servicing.
Documented causes: Status of battery charging system (failure). See the table for the matching fixes.