Generator: onan
Read the code first
On many Onan RV sets the status light blinks the first digit, pauses, then blinks the second digit. Write the full number down BEFORE you cycle power. Confirm the model and spec letter because meanings can vary.
5 checks before codes
Fuel in the tank, fuel valve open, no leak
Oil level and oil change interval
Air filter clean and the intake clear
Start battery strong (a weak battery causes many starting faults)
Exhaust, spark arrestor and compartment vents clear
Codes
36|Engine stopped without a stop command|Check the fuel level, prime for about 30 seconds per the manual, and check the air filter. Stop if you find a fuel leak or damage.
12|Output over voltage|Generator output too high. Disconnect loads, check the voltage regulation and sensing, then service.
13|Output under voltage|Overloaded, engine running slow, or a weak alternator. Reduce the load, check engine speed, service.
14|Output over frequency|Engine speed too high. Check the governor and throttle actuator and linkage.
15|Output under frequency|Engine running slow or overloaded. Fuel, air, load and the governor.
19|Throttle actuator circuit fault|Check the actuator plug and wiring, and the linkage for binding. Replace the actuator if needed.
25|Alternator over voltage|Alternator control fault. Service.
26|Alternator under voltage|Alternator, wiring or load problem. Check load, then service.
27|PMA sense lost|The permanent magnet alternator signal is lost. Check the plug and wiring, then the alternator.
29|Battery over voltage|Check the start battery and the charge circuit. Measure the battery while running.
Common Onan problems
Old fuel and a gummed carburetor (stores badly). Clogged air filter. Dirty spark arrestor. Weak start battery or loose battery cables. Fuel pump or filter. Low oil shutdown. Overload or a load that starts too hard (AC compressor).
Stops under load: carburetor, fuel supply, overload, or a dirty spark arrestor. Runs rough: carburetor, plug, air. Starts, then dies: fuel prime, fuel pump, or a safety shutdown.
Output check (for the tech)
At the outlet, no load: about 120 V and about 60 to 62 Hz is typical. Under load it should stay about 108 to 132 V and near 60 Hz. Wide swings mean the governor or fuel.
Carbon monoxide. Run generators with the exhaust clear and never with a blocked compartment. Test the CO alarm.
Fuel leak or fuel smell: stop. Fix the leak before running it.