Cummins/Onan 4.0 KY troubleshooting: 39 fault codes and symptom-cause-remedy entries from the manufacturer's own service documentation.
Cummins/Onan 4.0 KY — full specs, parts & maintenance.
All Cummins/Onan fault codes →
| Code | Meaning | Cause | Remedy |
|---|---|---|---|
| 3 | Service Check | See second-level fault code. | |
| 4 | Over Crank | Cranking exceeded 30 seconds without engine starting. | A. Check Fuel Level 1. If fuel level is low, fill the fuel tank. B. Check LPG Level Check and fill the LPG container, as necessary. C. Check Spark Plug(s) 1. Secure the spark plug lead(s) on the spark plug(s). 2. Replace the spark plug(s). D. Check Air Filter Element Replace the air filter if dirty. E. Replace Engine Oil Replace engine oil with oil of proper viscosity for the ambient temperature. F. Check Fuel Fittings 1. Tighten any fuel fitting if there is a fuel or air leak. 2. Reprime the engine fuel system by positioning the control switch to STOP/PRIME for 30 seconds. G. Replace Fuel Filter |
| 12 | Over Voltage | A. Contact Local Dealer or Distributor | |
| 13 | Under Voltage | A. Reduce Load Reduce the number of connected appliances, especially air conditioners and battery chargers. (Review load management in Loading the Generator Set.) | |
| 14 | Over Frequency | A. Contact Local Dealer or Distributor | |
| 15 | Under Frequency | A. Reduce Load Reduce the number of connected appliances, especially air conditioners. | |
| Code 27 | Indicates the control is unable to sense output voltage. | A. Contact Local Dealer or Distributor | |
| Code 29 | Indicates that voltage across the battery system is greater than 19 Volts. | A. Check Battery 1. Check battery bank connections and reconnect if necessary so that the 12 Volt batteries serving the generator set are connected in parallel (12 Volt) rather than in series (24 Volt). 2. Select a lower battery boost charge rate. | |
| Code 32 | Indicates that cranking speed is less than 180 RPM for more than 2 seconds. | A. Check Battery 1. Clean and tighten the positive (+) and negative (–) battery cable connections at the battery and at the generator set. 2. Recharge or replace the battery. Refer to the battery manufacturer's recommendations. B. Replace Engine Oil Replace engine oil with oil of proper viscosity for the ambient temperature. NOTICE: High oil viscosity can slow down cranking speed. | |
| Code 35 | Indicates that a microprocessor EEPROM error occurred during self test. | A. Contact Local Dealer or Distributor | |
| Code 36 | Indicates that the engine stopped without receiving a command from the control. | A. Check Fuel Level 1. If fuel level is low, fill the fuel tank. NOTICE: The generator set fuel pickup tube could be higher up in the fuel tank than the vehicle engine pickup. 2. Prime the engine fuel system by positioning the control switch to STOP/PRIME for 30 seconds. B. Check LPG Level Check and fill the LPG container, as necessary. NOTICE: On cold days, the LPG container may have to be kept at least half full to provide the rate of vaporization necessary to keep up with the generator set fuel demand. C. Check Spark Plug(s) 1. Secure the spark plug lead(s) on the spark plug(s). 2. Replace the spark plug(s). | |
| Code 37 | Indicates that the frequency/RPM ratio is wrong. | A. Contact Local Dealer or Distributor | |
| Code 38 | Indicates low power factor loads. | A. Reduce Load Reduce the number of connected appliances, especially air conditioners and battery chargers. (Review load management in Loading the Generator Set.) B. Check Appliances for Proper Operation Have air conditioners and other appliances checked for proper operation. | |
| Code 41 | Indicates control is unable to sense field or output voltage. | A. Contact Local Dealer or Distributor | |
| Code 42 | Indicates that a microprocessor ROM error occurred during self test. | A. Contact Local Dealer or Distributor | |
| Code 43 | Indicates that a microprocessor RAM error occurred during self test. | A. Contact Local Dealer or Distributor | |
| Code 45 | Indicates the control is unable to sense quadrature frequency. | A. Contact Local Dealer or Distributor | |
| Code 47 | Indicates the control is unable to sense ignition. | A. Contact Local Dealer or Distributor | |
| Code 48 | Indicates the control is unable to sense field voltage. | A. Contact Local Dealer or Distributor |
| Symptom | Cause | Remedy |
|---|---|---|
| Dizziness | GET OUT INTO THE FRESH AIR IMMEDIATELY. If symptoms persist, seek medical attention. Shut down the genset and do not operate it until it has been inspected and repaired. | |
| Muscular Twitching | GET OUT INTO THE FRESH AIR IMMEDIATELY. If symptoms persist, seek medical attention. Shut down the genset and do not operate it until it has been inspected and repaired. | |
| Vomiting | GET OUT INTO THE FRESH AIR IMMEDIATELY. If symptoms persist, seek medical attention. Shut down the genset and do not operate it until it has been inspected and repaired. | |
| Weakness and Sleepiness | GET OUT INTO THE FRESH AIR IMMEDIATELY. If symptoms persist, seek medical attention. Shut down the genset and do not operate it until it has been inspected and repaired. | |
| Inability to Think Coherently | GET OUT INTO THE FRESH AIR IMMEDIATELY. If symptoms persist, seek medical attention. Shut down the genset and do not operate it until it has been inspected and repaired. | |
| 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. | A. Try running with fewer appliances connected. See Powering Equipment. b. Check the fuel tank (LPG models) and fill as necessary. On cold days the LPG container may have to be kept at least half full to provide the rate of vaporization necessary to keep up with the genset fuel demand. | |
| 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 vehicle power cord into the genset power output receptacle (if so equipped) or turn the vehicle 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. | |
| Status Indicator Not Working | Indicates that there could be faulty connections or no battery voltage. | A. Check Other Control Switch Try the generator set control switch if the remote control switch start doesn't work, and vice versa. B. Check Battery 1. Clean and tighten the positive (+) and negative (–) battery cable connections at the battery and at the generator set. 2. Recharge or replace the battery. Refer to the battery manufacturer's recommendations. |
| Starting Batteries Run Down | Indicates problem with batteries, connections, charging system, or parasitic loads. | A. Check Battery 1. Clean and tighten the positive (+) and negative (–) battery cable connections at the battery and at the generator set. 2. Recharge or replace the battery. Refer to the battery manufacturer's recommendations. B. Battery Charging System Install or service a battery charging system in the vehicle. |
| Starter Engages-Disengages | Indicates cranking voltage dips below 6 Volts. | A. Use Vehicle to Start Generator Set Run the vehicle propulsion engine while trying to start the generator set—the battery charging alternator may be able to maintain starting voltage high enough to start the generator set. B. Check Battery 1. Clean and tighten the positive (+) and negative (–) battery cable connections at the battery and at the generator set. 2. Recharge or replace the battery. Refer to the battery manufacturer's recommendations. C. Change Battery Cables Increase battery cable size or run parallel cables. |
| Status Indicator Goes Out While Cranking—No Start | Indicates an internal short circuit caused an automatic-reset circuit protective device to trip. | A. Try Starting Again If the status indicator flashes and goes out again without the engine starting, call local dealer or distributor. |
| No Power—Generator Set Running, Status Light On | Indicates line circuit breaker is OFF, or tripped due to short circuit or overload. | A. Check Line Circuit Breakers 1. Turn on or reset the line circuit breaker on the generator set. 2. Turn on or reset the line circuit breaker on the main distribution panel in the vehicle. |
| The status indicator blinks, indicating a fault. | See Chapter 6 on page 43 if the generator set shuts down and the status indicator blinks, indicating a fault. | |
| Cranking will stop in approximately 30 seconds. The status indicator will blink, indicating an over crank fault. | Wait 5 seconds for the control to reset before trying again. After 5 tries, let the starter motor cool down for 30 seconds before trying again. |
Fault codes and symptom→remedy steps extracted from this model’s service/owner documentation; verify against the official manual before servicing.
Documented causes: Cranking exceeded 30 seconds without engine starting.. See the table for the matching fixes.
Documented causes: Indicates that there could be faulty connections or no battery voltage.. See the table for the matching fixes.
Documented causes: Indicates problem with batteries, connections, charging system, or parasitic loads.. See the table for the matching fixes.