Onan Generator Troubleshooting; 13 Tips for RV Generator Repair

Onan is known for its standby generators. However, they also make portable generators, especially those that go in RVs. Many Onan generator models can run on gasoline and liquid propane. Their generators are typically compact and relatively quiet. They often sell generators in portable shells that protect them while muffling the sounds it makes.

Their generators regularly come with intelligent control boards capable of self-diagnostics, while most units have an integrated design that is incredibly easy to connect to your RV. That is aside from the fact that Onan generators are often built into the RV by the manufacturer.

Here are our top 13 tips for getting the most of out your Onan generator troubleshooting fixed.

How to Troubleshoot Onan Generator? Here, 13 Ways

Tip 01. Understand the brand’s evolution.

Onan is one of the top selling generator brands in the United States. However, the brand has been picked up by Cummins. That’s why you now see products listed as Cummins Onan or Cummins part number Onan.

This means that you may have to search for the Onan part number in the Cummins inventory listed on a website. That’s especially true for consumable parts like spark plugs and air filters.

For example, the Onan generator manufacturer’s home page is now www.cumminsonan.com.

Tip 02. Check the fuel levels.

If your Onan generator isn’t running, it may be because fuel levels are too low. While some RV generators will run until the fuel tank has nothing but fumes, the Onan models tend to stop working when you’re down to a quarter tank. The units that do this are the ones drawing from the gas tank.

The intent is to ensure that the RV isn’t stranded because you have no gas in the tank. In the future, top off your RV gas tank so that it never runs low. And know that the generator will shut down if the gas gauge is around one quarter. 

Note that you can really run into problems if the gas tank float is off, so the generator turns off though you have a half-full tank.

Tip 03. Pay attention to safety features.

Onan generators have a number of built-in safety features. One of these is the fuel cut-off switch so you don’t use all your gas running power though it would leave you stranded on the side of the road.

Another is the low oil cut-off. If the generator is cutting off, check the oil levels. You can avoid problems by making sure the oil tank is full. It also means that an oil leak in the generator can kill it well before the unit suffers damage.

If the safety feature trips and the generator is giving you an error code, look it up before assuming that resetting the generator is all you need to do. For example, issues that make a generator run rough could be deal with temporarily, but the long-term damage will destroy the generator.

Tip 04. Know your generator codes.

Onan generators are among the smartest on the market. They can self-diagnose issues. However, it won’t tell you outright it thinks the oil is low. Instead, it flashes codes to indicate the problem.

One solution is to check the manual. What if you don’t have the manual? Then you can go to www.cumminsonan.com and look up the error codes. Even the error codes for older and rare Onan generators can be looked up on that site.

Tip 05. Know the maintenance needs of your Onan generator.

Onan has made a number of design changes that simplify maintenance. For example, the Onan 4K generator doesn’t have an oil filter. On the other hand, you have to use the right oil and never use old oil to keep the generator from clogging up.

Know the right level of oil, because over-filling will cause the generator to shut off just as too much would. Know where you would access the carburetor if you need to clean it and where you access other points required for maintenance.

Tip 06. Know your RV.

In some cases, you have to restart the line breaker in the RV to get the power going after you’ve done maintenance on the generator. This is because of the safety features built into the RV after you’ve lost power, even if it was because you disconnected the battery while working on the generator.

Always know where the circuit breakers and other electrical panels are so that you can reset or repair things as necessary.

Tip 07. Know the benefits of a dual fuel generator.

Do you have a dual fuel generator in your RV? For example, some Onan generators can run off both gasoline and liquid propane. This allows you to conserve gasoline when you’re away from civilization.

And it allows you to switch to another fuel source to see if the root cause of it shutting down is a low gas level. For example, switch to propane if the gas tank is getting low. And consider carrying extra propane tanks in addition to gas cans.

Tip 08. Plan for peak loads to avoid problems.

Do you need extra air conditioning in your RV to stay comfortable? Onan generators don’t have the same peak load / surge capacity as some inverter generators. This means you should turn on the RV generator before you turn on the roof-top AC to avoid tripping electrical safeties.

And don’t try to turn on too many things at once, since that can cause surges that trip the safety measures like the over-voltage protection.

Tip 09. Know your power capacity.

Onan generators are often powerful. For example, you can find units that can power one or two air conditioners. However, they don’t always have excess capacity. Know how much power the generator can supply and the load everything you’re running in the RV will draw.

For example, you may be able to run the air conditioner at full blast and the refrigerator at the same time but not the microwave, too.

The 7000 watt Onan RV generators may seem like they can run everything in the RV, but you can cause it to trip safeties if you try to do too much. The over voltage protections in particular tend to engage when you walk into the RV and turn everything on.

Tip 10. Service varies. Plan accordingly.

Onan itself is known for high quality generators. Onan is relying on network of contracted dealers to provide service for most of their RV generators. Service levels vary between mechanics and RV shops.

Do your research before you bring in your RV for service. And verify that the RV shop is experienced working with Onan Cummins generators. Just because they can work with other brands doesn’t mean they know how to repair Onan Cummins generators.

While the Onan RV generators are an industry standard, not all service providers can and will have replacement parts in stock.

Tip 11. Understand the value of various labels and certifications.

In most cases, your Onan generator is USDA Forest Service Approved. Do you know what that means? Why yes, Mr. Forest Ranger, we are allowed to run the generator in our RV while we’re parked in sensitive national parks, because we know it can’t accidentally spark a wildfire.

Nearly all Onan generators also meet the National Park Service sound level requirement. That is 60 decibels of noise or less at a distance of fifty feet. These rules may allow you to run your generator later at night in RV parks with noise limits, too, but you should know their rules rather than assuming you’re already compliant.

Tip 12. Pay attention to the warranties.

Onan warranties depend on the application. For example, it is common to see a three year or 2000 hour warranty on an Onan generator. If you’re running it nearly all day every day, that means you’ve blown through the warranty in a year.

Another issue is the application. The Onan generator’s three year limited warranty is when it is in the RV and only powering the RV. If you take it out of the RV and use it to provide backup power for your home, the warranty is two years at most.

If you put an RV generator in your shed and use it as a backup power source, it will then have the two year non-RV warranty in place if it applies at all. Find out what the warranty will be from the supplier.

Tip 13. Use good gas/oil/fuel.

We already mentioned that Onan generators sometimes don’t have oil filters. They generally have fuel filters. However, those are not always easy to replace and can be expensive. This makes using quality consumables.

Don’t put old gas or watery gas in your generator. Only use high quality gas, though this doesn’t mean you have to use premium gasoline.

This also means you’ll get extra mileage out of the generator if you use a good fuel injector cleaner periodically. While that adds to the cost of your maintenance routine, it is a necessity because Onan generators are designed to run smoothly on high quality intakes.

If you did use cheap gas or the wrong fuel, clean everything immediately to avoid problems.


The odds are high that your RV generator is an Onan Cummins or original Onan model. Know how to sustain, maintain and repair common issues with the generator to minimize trips to the mechanic and maximize the running life of the most important equipment in the RV aside from the car motor.

John S.

Hello guys! I'm a 37-years-old author, traveler, writer, blogger, and a camper. I enjoy life as much as I can and love to visit beautiful places in my RV. That's why while traveling I have decided to dedicate some time to share my experiences with everyone that might be interested in traveling, camping, and RVs.