Onan Standby Generators Error Codes

Code 11

Generator cranks but will not start; fault light on, and Code 11 is displayed or flashed

No Crank Signal / Start Command Fault

Code 12

Generator cranks but will not start; Code 12 is displayed, indicating low cranking speed

Low Cranking Speed / Low Battery Voltage

Code 13

Generator shuts down shortly after start; Code 13 is displayed for a governor actuator or speed control fault

Governor Actuator / Speed Control Failure

Code 14

Generator shuts down; Code 14 is displayed, indicating an over-speed condition

Engine Overspeed Protection Trip

Code 15

Generator shuts down; Code 15 is displayed for an under-speed condition

Engine Underspeed / Load Too High

Code 19

Generator shuts down during crank or shortly after start; Code 19 is displayed for governor actuator overcurrent

Governor Actuator Overcurrent / Short

Code 23

Generator shuts down; Code 23 is displayed, indicating low oil pressure

Low Oil Pressure Shutdown

Code 24

Generator shuts down; Code 24 is displayed, indicating high engine temperature

High Coolant Temperature / Overheat

Code 25

Generator shuts down; Code 25 is displayed, indicating high exhaust temperature

High Exhaust Temperature Shutdown

Code 27

Generator shuts down; Code 27 displayed, indicating voltage sense loss or abnormal AC output.

AC Voltage Sense Fault

Code 29

Generator shuts down; Code 29 displayed, indicating low voltage output.

Low AC Output Voltage

Code 31

Generator shuts down; Code 31 displayed, indicating overspeed or frequency too high.

High Frequency / Overspeed Fault

Code 32

Generator shuts down; Code 32 displayed, indicating low cranking speed or failure to start.

Failure to Start / Low Cranking Speed

Code 33

Generator shuts down; Code 33 displayed, indicating overcrank (too many failed start attempts).

Overcrank / Failure to Start

Code 34

Generator shuts down; Code 34 displayed, indicating low frequency.

Low Frequency / Underspeed

Code 36

Generator shuts down; Code 36 displayed, indicating the engine stopped without a shutdown command.

Engine Stopped Unexpectedly

Code 37

Generator shuts down; Code 37 displayed, indicating voltage imbalance or phase error (3-phase units).

Phase Voltage Imbalance / Phase Loss

Code 38

Generator shuts down; Code 38 displayed, indicating overcurrent or a short circuit.

Overcurrent / Short Circuit Protection Trip

Code 41

Generator shuts down; Code 41 displayed, indicating loss of engine speed signal.

Loss of Engine Speed Signal

Code 42

Generator shuts down; Code 42 displayed, indicating loss of field or excitation.

Loss of Excitation / Field Circuit Fault

Code 43

Generator shuts down; Code 43 displayed, indicating DC overvoltage.

DC Bus Overvoltage

Code 44

Generator shuts down; Code 44 displayed, indicating DC undervoltage.

DC Bus Undervoltage / Low Battery

Code 45

Generator shuts down; Code 45 displayed, indicating low fuel level (if equipped with a level sensor).

Low Fuel Level Shutdown

Code 47

Generator shuts down; Code 47 displayed, indicating a fuel solenoid circuit fault.

Fuel Shutoff Solenoid Circuit Failure

Code 51

Generator shuts down; Code 51 displayed, indicating an intake air heater fault (diesel units).

Intake Air Heater Circuit Failure

Code 54

Generator shuts down; Code 54 displayed, indicating a CAN communication fault (on newer digital models).

CAN Bus Communication Error

Symptom

Fuel leak observed around the generator, or a smell of fuel in the enclosure.

External Fuel Leak.

Symptom

Generator cranks normally but does not fire or start; no specific code is shown.

No Start – Fuel or Ignition Failure

Symptom

Generator emits blue smoke from the exhaust, especially under load.

Oil Burning / Internal Engine Wear.

Symptom

Generator emits excessive black smoke from the exhaust during operation.

Rich Fuel Mixture / Incomplete Combustion (Diesel or Gas).

Symptom

Generator emits white smoke, especially on startup.

Incomplete Combustion / Coolant or Fuel Issue.

Symptom

Generator is excessively noisy during operation (mechanical knocking or rattling).

Abnormal Mechanical Noise.

Symptom

Generator produces power, but voltage is unstable or fluctuates under load.

Unstable Voltage Regulation.

Symptom

Generator runs but does not produce AC power at the terminals.

No AC Output / Loss of Excitation.

Symptom

Generator runs, but frequency (Hz) is too low or too high.

Incorrect Engine Speed / Frequency Out of Spec.

Symptom

Generator starts then shuts down after a few seconds, with no load applied and no clear code.

Run-Then-Stop – Safety Circuit or Fuel Issue

Symptom

Generator vibrates excessively, causing the enclosure or nearby structures to shake.

Excessive Vibration.

Symptom

Generator will not start; no error code displayed, and the panel appears dead.

No DC Power to Control Panel

Symptom

Oil leak visible under the generator or on engine surfaces.

External Engine Oil Leak.

Symptom

Strong fuel odor around the generator during or after operation, with no visible leak.

Fuel Vapor Leakage / Venting Issue

Symptom

The automatic transfer switch does not transfer the load to the generator when it is running.

Transfer Switch Fails to Transfer

Symptom

The control panel display is dim, unreadable, or has missing segments.

Display / HMI Failure

Symptom

The generator battery repeatedly goes dead between exercise cycles or outages.

Chronic Battery Discharge / Charging System Issue

Symptom

The generator does not start automatically during a utility power outage, but starts manually.

Auto-Start / Remote Start Failure

Symptom

The generator enclosure becomes excessively hot, and components show heat discoloration.

Inadequate Ventilation / Cooling Airflow Restriction