Cummins/Onan 4KY troubleshooting: 42 fault codes and symptom-cause-remedy entries from the manufacturer's own service documentation.
Cummins/Onan 4KY — full specs, parts & maintenance.
All Cummins/Onan fault codes →
| Code | Meaning | Remedy |
|---|---|---|
| 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. |
| NO. 38 | OVERCURRENT FAULT—CODE NO. 38 (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.) |
| NO. 41 | GENERATOR ROTOR FAULT—CODE NO. 41 (Controller unable to sense field or output voltage) | See an authorized Onan dealer. |
| NO. 42 | PROCESSOR FAULT—CODE NO. 42 (Microprocessor ROM error during self-test) | See an authorized Onan dealer. |
| NO. 43 | PROCESSOR FAULT—CODE NO. 43 (Microprocessor RAM error during self-test) | See an authorized Onan dealer. |
| NO. 45 | SPEED SENSE FAULT—CODE NO. 45 (Controller unable to sense quadrature frequency) | See an authorized Onan dealer. |
| NO. 47 | IGNITION FAULT—CODE NO. 47 (Controller unable to sense ignition) | See an authorized Onan dealer. |
| NO. 48 | GENERATOR FIELD SENSE FAULT—CODE NO. 48 (Controller unable to sense field voltage) | See an authorized Onan dealer. |
| 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 |
|---|---|---|
| Generator output connections must be made by a qualified electrician | Make generator output connections only by a qualified electrician in accordance with applicable codes. | |
| The genset must not be connected to the public utility or any other source of electrical power. | Do not connect the genset to the public utility or any other source of electrical power. Use an approved switching device to prevent interconnections. | |
| Generator sets use substances that can cause health risks | Use appropriate personal protective equipment when exposed to fuel, oil, coolant, wet batteries, grease, cleaning agents, or other substances. Use proper containers for transport, storage, and disposal of waste substances. Follow local regulations. | |
| STARTING BATTERIES RUN DOWN | (Marginal batteries, connections, or charging system or, parasitic loads) | 1. Clean and tighten the positive (+) and negative (−) battery cable connections at the battery, vehicle frame and genset. 2. Recharge or replace the battery. Refer to the battery manufacturer’s recommendations. 3. Have a battery charging system installed or serviced in the vehicle. |
| STARTER ENGAGES-DISENGAGES | (Cranking voltage dips below 6 volts—low battery charge, poor connections, long cables) | 1. 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. 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. 4. 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) | 1. Turn on or reset the line circuit breaker on the genset (Page 2-3). 2. Turn on or reset the line circuit breakers on the main distribution panel in the vehicle. |
| 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 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: (Marginal batteries, connections, or charging system or, parasitic loads). See the table for the matching fixes.
Documented causes: (Cranking voltage dips below 6 volts—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.