Cummins/Onan 3.6KY troubleshooting: 29 fault codes and symptom-cause-remedy entries from the manufacturer's own service documentation.
Cummins/Onan 3.6KY — full specs, parts & maintenance.
All Cummins/Onan fault codes →
| Code | Meaning | Remedy |
|---|---|---|
| 3 | Service Check Fault | |
| 4 | Overcrank | |
| 12 | Overvoltage | |
| 13 | Undervoltage | |
| 14 | Overfrequency | |
| 15 | Underfrequency | |
| 27 | Voltage Sense Lost | |
| 29 | High Battery Voltage | |
| 32 | Low Cranking Speed Sense | |
| 33 | Fault Code 33 | |
| 35 | Control Card Failure | |
| 36 | Genset Stopped Without Fault Condition | |
| 38 | Field Overload (Overvoltage) | |
| 41 | Generator Rotor Fault | |
| 42 | Processor Fault | |
| 45 | Speed Sense Fault | |
| 48 | Field Sense Fault | |
| 51 | Processor Failure | |
| CODE NO. 38 | OVERCURRENT FAULT—Low power factor loads | 1. Reduce the number of appliances running at the same time, especially those with high motor starting loads such as air conditioners. 2. Have air conditioners and other appliances checked for proper operation. (A locked compressor rotor can cause very low power factor.) |
| CODE NO. 41 | GENERATOR ROTOR FAULT—Controller unable to sense field or output voltage | See an authorized Onan dealer. |
| CODE NO. 42 | PROCESSOR FAULT—Microprocessor ROM error during self-test | See an authorized Onan dealer. |
| CODE NO. 43 | PROCESSOR FAULT—Microprocessor RAM error during self-test | See an authorized Onan dealer. |
| CODE NO. 45 | SPEED SENSE FAULT—Controller unable to sense quadrature frequency | See an authorized Onan dealer. |
| CODE NO. 47 | IGNITION FAULT—Controller unable to sense ignition | See an authorized Onan dealer. |
| CODE NO. 48 | GENERATOR FIELD SENSE FAULT—Controller unable to sense field voltage | See an authorized Onan dealer. |
| Symptom | Cause | Remedy |
|---|---|---|
| Cranking voltage dips below 6 volts | Low battery charge, poor connections, long cables | Have the vehicle propulsion engine running while trying to start the genset—the battery charging alternator may be able to maintain starting voltage high enough to get the genset started. Clean and tighten the positive (+) and negative (−) battery cable connections at the battery, vehicle frame and genset. Recharge or replace the battery. Refer to the battery manufacturer’s recommendations. Increase battery cable size or run parallel cables. |
| STATUS INDICATOR LIGHT GOES OUT WHILE CRANKING—NO START | Internal short circuit caused automatic-reset circuit protective device to trip | Try starting again. See an authorized Onan dealer if the status indicator light flashes and then goes out again without the engine starting. |
| NO POWER—GENSET RUNNING, STATUS LIGHT ON | Line circuit breaker OFF, or tripped due to short circuit or overload | Turn on or reset the line circuit breaker on the genset (Page 2-3). Turn on or reset the line circuit breakers on the main distribution panel in the vehicle. |
| STATUS INDICATOR LIGHT DEAD (Faulty connections, no battery voltage) | 1. Try the genset Start Switch if the remote Start Switch does not work, and vice versa. 2. Clean and tighten the positive (+) and negative (−) battery cable connections at the battery, vehicle frame and genset. 3. Recharge or replace the battery. Refer to the battery manufacturer’s recommendations. |
Fault codes and symptom→remedy steps extracted from this model’s service/owner documentation; verify against the official manual before servicing.
Documented causes: Low battery charge, poor connections, long cables. See the table for the matching fixes.
Documented causes: Internal short circuit caused automatic-reset circuit protective device to trip. See the table for the matching fixes.
Documented causes: Line circuit breaker OFF, or tripped due to short circuit or overload. See the table for the matching fixes.