Cummins/Onan 4MKY troubleshooting: 27 fault codes and symptom-cause-remedy entries from the manufacturer's own service documentation.
Cummins/Onan 4MKY — full specs, parts & maintenance.
All Cummins/Onan fault codes →
| Code | Meaning | Remedy |
|---|---|---|
| 3 | SERVICE CHECK FAULT—CODE NO. 3 | Check the second-level fault code by pressing STOP once. The second-level fault code will have two-digits. The faults are listed in numerical order in this table. |
| 4 | OVERCRANK FAULT—CODE NO. 4 | 1. Check and fill the fuel tank, as necessary. (Note: The genset fuel pickup is probably higher than the boat engine pickup.) 2. Prime the engine fuel system by holding the control switch at Stop/Prime for 30 seconds. 3. Open any closed fuel valves. 4. Secure the spark plug lead on the spark plug (Page 20). 5. Replace the spark plug (Page 20). 6. Service the air cleaner (Page 19). |
| 12 | OVERVOLTAGE FAULT—CODE NO. 12 | See an authorized Onan dealer. |
| 13 | UNDERVOLTAGE FAULT—CODE NO. 13 | Reduce the number of connected appliances, especially when air conditioners and battery chargers are running. |
| 14 | OVERFREQUENCY FAULT—CODE NO. 14 | See an authorized Onan dealer. |
| 15 | UNDERFREQUENCY FAULT—CODE NO. 15 | Reduce the number of connected appliances, especially when air conditioners and battery chargers are running. |
| 27 | VOLTAGE SENSE FAULT—CODE NO. 27 | See an authorized Onan dealer. |
| 29 | HIGH BATTERY VOLTAGE FAULT—CODE NO. 29 | 1. Check battery bank connections and reconnect if necessary so that the 12 volt batteries serving the genset are connected in parallel (12 v |
| CODE NO. 32 | LOW CRANKING SPEED FAULT—Cranking speed less than 180 rpm for more than 2 seconds | 1. Clean and tighten the positive (+) and negative (−) battery cable connections at the battery and at the genset. 2. Recharge or replace the battery. Refer to the battery manufacturer’s recommendations. 3. Replace engine oil with oil of proper viscosity for ambient temperatures (Page 7). (High oil viscosity can slow down cranking speed.) |
| CODE NO. 35 | CONTROL CARD FAILURE FAULT—Microprocessor EEPROM error during self-test | See an authorized Onan dealer. |
| CODE NO. 36 | ENGINE STOPPED FAULT—Engine stopped without command by controller | 1. Check and fill the fuel tank, as necessary. (Note: The genset fuel pickup is probably higher than the boat engine pickup.) 2. Secure the spark plug lead on the spark plug (Page 20). 3. Replace the spark plug (Page 20). 4. Service the air cleaner (Page 19). 5. Check for mechanical damage. |
| CODE NO. 37 | INVALID GENSET CONFIGURATION FAULT—Genset configuration is preprogrammed at the factory | See an authorized Onan dealer. |
| 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 | Remedy |
|---|---|
| The engine fails to crank. | A. Try starting at the genset rather than at the remote control. b. Replace the fuse on the control panel if it has blown. c. Clean and tighten the positive (+) and negative (- ) battery cable connections at the battery and the genset. d. Recharge the battery. Refer to the battery manufacturer’s recommendations. |
| The engine cranks slowly. | A. Disconnect the air conditioner and other large loads. b. Clean and tighten the positive (+) and negative (- ) battery cable connections at the battery and the genset. c. Recharge the battery. Refer to the battery manufacturer’s recommendations. d. Change the engine oil to oil having the proper viscosity for the ambient temperature. See Table 1. |
| The engine cranks but fails to start. | A. Check the fuel tank and fill if necessary. b. Open any closed fuel shut off valve. c. Check engine oil level and add oil as necessary. d. Service the air cleaner. e. Secure the spark plug lead on the spark plug. f. Replace the spark plug. |
| The engine runs and then stops or surges. | A. Check the fuel tank and fill if necessary. b. Check the engine oil level and add oil as necessary. Drain excess oil if the level is above the dipstick Full mark. c. Check and reset the carburetor altitude adjust knob. See Varying Operating Conditions. (Gasoline models only.) d. Secure the spark plug lead on the spark plug. e. Replace the spark plug. |
| The genset keeps stalling or the circuit breaker keeps tripping. | Try running with fewer appliances connected. See Powering Equipment. |
| There is no electrical power even though the genset runs. | A. Reset tripped circuit breakers. See Powering Equipment. b. Unless there is an automatic power transfer switch, plug the boat power cord into the genset power output receptacle (if so equipped) or turn the boat power selector switch to its genset position (if so equipped). |
| The remote battery condition meter indicates low voltage. | A. Clean and tighten the positive (+) and negative (- ) battery cable connections at the battery and the genset. b. Recharge the battery. Refer to the battery manufacturer’s recommendations. |
| Black smoke exits the tailpipe. | Service the air cleaner. |
Fault codes and symptom→remedy steps extracted from this model’s service/owner documentation; verify against the official manual before servicing.