Onan generator keeps shutting off (quits after a few minutes)

Common symptoms

• It starts fine, then keeps dying after 5 or 10 minutes.
• It dies the moment the air conditioner kicks on.
• It stops when you let go of the START switch.
• It runs a while, shuts down, and restarts only after it cools off.
• The light on the start switch blinks a pattern after it stops.

Quick checks before anything else

• Count the blinks on the status light before you touch anything else.
• Fill the RV fuel tank, even if the gauge shows fuel left.
• Check the oil on level ground with the generator stopped.
• Turn off the air conditioners and battery chargers, then restart.
• Clear anything blocking the air openings and the tailpipe.
• On a diesel, check the coolant level once the engine is cool.

What makes an Onan generator shut itself off?

• Fuel below the generator pickup The generator draws from higher in the shared tank, so it starves while the gauge still shows fuel. Usually code 36.
• Too much load Two air conditioners, a battery charger and a microwave add up fast. Codes 13, 15, 22 or 38.
• Low oil The oil switch shuts it down to save the engine. Two blinks on most models, code 6 on inverter models.
• Heat Blocked air openings, dirty radiator fins on a diesel, or a hot day under heavy load. Code 1, or 34 for the inverter itself.
• Plug, air filter or exhaust A loose plug wire, worn plug, dirty air filter or blocked tailpipe. Code 36 or 22.

Step-by-step: when your Onan generator keeps shutting off

Start with the code, then work from fuel to load to heat. Cummins says keeping the oil topped up, keeping battery connections clean and tight, watching the fuel gauge and not overloading the generator prevent most shutdowns.

1. Read the code at the generator Count the blinks as soon as it stops. The last fault keeps flashing even after the problem is fixed, so don’t take an old code for a new one. If you have a remote panel inside and it shows nothing, the QG 2800i manual says to read the code at the generator’s own switch. Then look it up in our Onan QG 5500 and 7000 code list or the list for your model.
2. Rule out fuel first Code 36 means the engine stopped without a command from the control. On gas QG models, Cummins’ first check is fuel level, because the generator’s pickup tube can sit higher in the tank than the engine’s. The 2800i manual says most RVs cut off generator fuel well before the gauge reads empty. Fill the tank, hold STOP/PRIME for 30 seconds, and start again. If it now runs, mark the gauge where it quit so you know next time.
3. Check the oil level Park level, stop the generator, and read the dipstick. Code 2 is low oil pressure on the QG 2800, 5500, 7000 and QD diesels, and Cummins lists two causes: oil too low, or oil above the full mark. Add or drain to bring it between the marks. The QG 2800i shows code 6 for low oil level. If the level is right and the code keeps coming back, stop using the generator and call a dealer.
4. Shed the load If it quits when the air conditioner starts, the load is the suspect. Cummins says an air conditioner can draw 3 to 4 times its normal 1,400 to 2,400 watts while it starts, and a battery charger can pull up to 3,000 watts on its own. Codes 13 and 15 mean the generator could not hold voltage or frequency under the load, and code 38 is an overload. Turn off the battery charger and extra loads, start the generator, then bring the air conditioners on one at a time. For code 38, Cummins also says to have the air conditioners checked for proper operation. If one AC alone knocks it down, read RV AC keeps tripping the breaker.
5. Account for heat and altitude Cummins says rated power drops about 1% for every 10°F above 77°F, and about 3.5% for every 1,000 feet of elevation. A load that ran fine at home on a cool day can be too much on a hot afternoon in the mountains. On QG 5500 and 7000 gas models in the HGJAB series, reset the carburetor’s altitude knob when you change elevation. Cummins warns that running at low altitude with a high altitude setting can cause power loss and overheating.
6. Clear the air openings If it runs a while, quits, and restarts only after it cools, think airflow. The 2800i manual names blocked cooling air for that exact symptom, along with fuel level. Check the intake vents for leaves and debris and make sure hot air has room to escape. On QD diesels, code 1 means coolant passed 239°F for 10 seconds: let it cool, check the coolant, clear the openings under the generator, and clean the radiator fins with compressed air or a gentle rinse. Cummins says not to use a pressure washer.

   

7. Check the spark plug, air filter and exhaust For code 36 on gas models, Cummins’ next checks are pushing the spark plug wire on firmly, replacing the plug, and replacing a dirty air filter. Code 22 on the QG 5500, 7000 and QD diesels means the engine has worked near full throttle too long, from too much load, a dirty air filter or a blocked exhaust. With the generator off and cool, look at the tailpipe for mud, nests or a crushed end.
8. Check auto start On the 2800i, Cummins lists an enabled automatic generator start (AGS) feature as a cause of a generator that starts, runs, then stops on its own. AGS is a remote panel feature that starts and stops the generator by itself. Turn it off while you troubleshoot so you know what the generator is doing on its own.
9. Hold START long enough If it dies the instant you let go of the switch, keep holding START until the status light goes from flashing to steady. The 2800i manual’s advice for “starts but stops when start switch is released” is to let it crank fully. The 7000i DF is different: hold START more than 3 seconds, then release and wait. If it still won’t stay running, our RV generator won’t start guide covers fuel and battery checks.

Code 36 differs by model

The same number means different things across Onan families, so check your nameplate before you act on it.

Overload also works differently on inverter models. On the 2800i, code 38 means the built-in “virtual breaker” tripped and the generator shut down; Cummins says no further action is needed before a restart, once the load is lower. Its physical breaker is a backup, and when that one trips the generator keeps running. On the QG 2800, 4000, 5500 and 7000 the line breaker works the same way: if it trips, the engine keeps running and the RV loses power. That is a different problem, covered in RV generator running but no power.

Gas QG models with propane add one more cause: on cold days the LP tank may need to stay at least half full to make vapor fast enough. Our RV generator repair guide has the oil, battery and output specs for each model.

When to call an RV tech

• Code 2 or code 6 comes back with the oil at the right level.
• Code 36 keeps returning with fresh fuel, a new plug and a clean air filter.
• Code 36 on a QG 4000i or 7000i DF, where the manual lists no owner fix.
• Codes 13, 15 or 38 come back with only a light load.
• A diesel keeps losing coolant, or code 1 returns with clear airflow.
• Knocking, smoke, or any fuel or exhaust leak.

Common questions