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Every Cummins Onan engine fault code in our verified reference — 26 codes, 17 of them with a documented remedy. Find your code in the table, read the likely causes, then work the remedy. If it is beyond a field fix, our workshop in Embakasi repairs Cummins Onan controllers and engines at board level.
Covers: 10RESV and 12RESV · 14RES/RESL and 20RES/RESL · Various
| Code | Fault | Likely cause | Remedy |
|---|---|---|---|
| 15 | Underfrequency Fault (Engine governor unable to maintain rated frequency). | Reduce the number of connected appliances; from a remote control or safety system) has been activated | — |
| 27 | Voltage Sense Fault (Controller unable to sense output voltage). | See an authorized Onan dealer.; triggering a shutdown. | — |
| 29 | High Battery Voltage Fault (Voltage across battery system greater than 19 volts). | causing a shutdown. | Check battery bank connections and reconnect if necessary so that the 12 volt batteries serving the genset are connected in parallel (12 volt) rather than in series (24 volt). Select a lower battery boost charge rate. |
| 32 | Low Cranking Speed Fault (Cranking speed less than 180 rpm for more than 2 seconds). | recommended fuel (e.g.; diesel). Inspect the fuel lines and tank for leaks. Verify the fuel level sensor and wiring for proper operation (e.g.; no shorts or opens). Clean or replace the sensor if necessary. Ensure the fuel supply system is functioning correctly. Reset the alarm on the control panel. to the SDMO if the alarm recurs. | Clean and tighten the positive (+) and negative (-) battery cable connections at the battery and at the genset. Recharge or replace the battery. to the battery manufacturer’s recommendations. Replace engine oil with oil of proper viscosity for ambient temperatures (High oil viscosity can slow down cranking speed).; Check the fuel level in the daily tank; refill with clean |
| 35 | Control Card Failure Fault (Microprocessor EEPROM error during self-test). | See an authorized Onan dealer.; triggering a shutdown. | — |
| 36 | Engine Stopped Fault (Engine stopped without command by controller). | Gasoline Models - Check and fill the fuel tank; as necessary. (Note: The genset fuel pickup tube is probably higher up in the fuel tank than the vehicle engine pickup.) LPG Models - Check and fill the LPG container; 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. Secure the spark plug lead on the spark plug. Replace the spark plug. Service the air cleaner. Check for mechanical damage.; causing a shutdown. | — |
| 37 | Invalid Genset Configuration Fault (Genset configuration is preprogrammed at the factory). | See an authorized Onan dealer.; Reduce the electrical load by disconnecting non-essential appliances. Inspect the alternator output wiring for shorts or loose connections. Check the load distribution and ensure it is within the generator’s rated capacity. Test the alternator for internal faults (e.g.; damaged windings). Reset the alarm on the control panel. If the alarm persists; consult the SDMO or a technician. | — |
| 38 | Overcurrent Fault (Low power factor loads). | Reduce the number of appliances running at the same time; especially those with high motor starting loads such as air conditioners. Have air conditioners and other appliances checked for proper operation. (A locked compressor rotor; for example; could cause very high starting currents.); causing a shutdown. | — |
| AC | Loss of AC sensing | Wiring Diagrams.; below 47 Hz for a 50 Hz system). | Check for loose connections. Check all AC leads connected to the controller for continuity. Wiring Diagrams. Alternator excitation failure: Inspect the brushes and check the FN and FP connections. Voltage Regulator failure: check for voltage on the output leads. Section 7 |
| AC Sens Loss | AC sensing lost | triggering a shutdown. | Check wiring and connections. Contact an authorized distributor/dealer for service if necessary |
| Accy PwrOver | Accessory Power Overload | indicating potential charging or battery issues. | Check wiring and connections. Contact an authorized distributor/dealer for service if necessary |
| AF | Auxiliary fault input | triggering a shutdown. | Check customer-supplied equipment. |
| Alt Protect | Alternator Protection. High generator current has been detected. The generator set shuts down to protect the alternator from damage caused by overheating the windings. | Reduce the load; preventing proper operation and triggering a shutdown. | — |
| ATS | ATS communication error | Section 7; Wiring Diagrams; Section 4.8.3. To clear the fault; disconnect and then reconnect battery power to the controller.; above 53 Hz for a 50 Hz system). | Check connection to Model RRT transfer switch interface board. Section 4.9.6 |
| ATS ComError | ATS communication error | indicating overcharging. | Check communication wiring between transfer switch interface board and generator set |
| ATS PhaseRot | ATS phase rotation mismatch | Correct the ATS connection. to the ATS Installation; risking damage and triggering a shutdown. | — |
| Aux Input | Auxiliary input | secure or clean as needed. Test the battery voltage | Check customer-supplied equipment; Verify the presence of the lithium battery in the control panel. Check battery connections for looseness or corrosion; replace if faulty or missing. Inspect wiring to the battery for breaks or shorts. Reset the alarm. Consult the SDMO or a technician if the alarm persists. |
| Batt Chg Flt | Battery charger fault | prime the system if needed. Inspect the battery voltage (ensure above 12.4V for 12V systems) and charge or replace if low. Verify the starter motor and solenoid for proper operation | Check external battery charger; Check the fuel level and ensure the fuel supply is open; check wiring for faults. Inspect the fuel system for air or blockages. Reset the fault and attempt to start. Consult the SDMO or a technician if unresolved. |
| Battery CrLo | Engine starting battery voltage critically low | faulty windings). Reset the alarm. to the SDMO or a technician if the issue persists. | Check the battery rating and condition. Check the battery charger operation. Charge or replace the battery; Check the electrical load for irregularities causing voltage spikes. Inspect the alternator voltage regulator for faults. Verify alternator output cables for shorts to power. Test the alternator for internal issues (e.g. |
| Battery High | Engine starting battery voltage high | reduce if exceeding the generator’s capacity. Inspect alternator output cables and connections for looseness or damage. Test the alternator voltage regulator for proper operation. Verify the alternator belt tension and condition. Reset the alarm. to the SDMO or contact a technician if the issue persists. | Check the battery rating and condition. Check the battery charger operation; Check the electrical load |
| Battery Low | Engine starting battery voltage low | triggering a shutdown. | Check the battery rating and condition. Check the battery charger operation. Charge or replace the battery |
| Eng Speed High | Engine speed high | triggering a shutdown. | Contact an authorized distributor/dealer |
| ESch | Exercise not scheduled | Press OFF to clear the warning. Set the exerciser at the RDC controller or at the transfer switch; if the Model RRT transfer switch is not used. NOTE: Exercise the generator set weekly. Section 4.6.; triggering a shutdown. | — |
| Hb | High battery voltage | opens; or loose connections. Verify the module is properly installed and powered. Reset the control panel and check communication. If the fault persists | Check the battery rating and condition. Battery mfr’s instructions. Check the battery charger operation. O/M.; Inspect the CAN bus wiring and connectors for the option 3 module for shorts; replace the module or consult the SDMO or a technician. |
| HE | High engine temperature | opens; or loose connections. Ensure the module is correctly installed and powered. Reset the control panel and verify communication. If unresolved | Check for blocked air inlets and exhaust outlets. 1.7.; Check the CAN bus wiring and connectors for the option 4 module for shorts; replace the module or to the SDMO or a technician. |
| Lb | Low battery voltage | opens; or loose connections. Confirm the module is properly installed and powered. Reset the control panel and check communication. If the fault persists | Check the battery rating and condition. Check the battery charger operation. Charge or replace the battery. Battery mfr’s instructions. O/M.; Inspect the CAN bus wiring and connectors for the option 5 module for shorts; replace the module or consult the SDMO or a technician. |
Codes and descriptions are industry-standard identifiers reproduced for identification only. This reference is not affiliated with or endorsed by Cummins Onan; for official procedures always refer to the manufacturer’s service manual for your specific engine. A dash means our registry holds no verified entry for that column — we publish the gap rather than fill it in.
Send us the code and the engine serial. We diagnose Cummins Onan sets on site across all 47 counties, and repair controllers at board level on the bench in Embakasi.