RV Generator Won’t Start Up? 6 Easy Things to Check First


Everyone wants to go camping and get away from it all, but many of us still want to have some basic electricity while doing it. An RV generator is a perfect way to meet your basic needs.

Unfortunately, the generator doesn’t always start like we want it to. Sometimes it will just refuse, and sometimes it will start and then stop.

This article will deal with manufacturer-installed generators (namely Onan, but other brands should be similar) and not generators that are powering the RV through the shore power cable. If you’re here for and external generator that won’t start or stalls shortly thereafter, I’ve still got you covered with my article here.

Generally, an RV generator will not start due to the RV fuel tank level being below 1/4, the RV being parked on uneven ground and triggering the low oil shutoff, a failure to prime the generator, stale fuel, or a weak battery.

Low Fuel Levels Will Cause an RV Generator to Start and Stop

If your generator is starting up just fine but quickly shutting off, it might actually be doing you a favor.

The RV and the generator both share the same gas tank, and the fuel distribution has been designed by the manufacturer to stop fuel flow to the generator around 1/4 to 3/8 of a tank. Somewhere in that range, your generator will cease to receive gasoline and will stall out immediately after starting in order to ensure that you have enough gasoline in your RV to make it to the next gas station.

Obviously, if you notice that your fuel level is in this range or below, the fix will be to simply add more fuel to the tank.

image showing how a low fuel tank will result in the RV generator not starting

Parking on Uneven Ground Will Stop Your RV Generator from Starting

Parking on an angle is not in an of itself the reason why your generator won’t start. The generator can absolutely run on an angle.

The problem with parking on uneven ground is when your oil level is also low.

Nearly all generators these days (RV generators and home models) have a low oil shutoff sensor in their crankcase.

There is a physical sensor that needs to be touching the oil in order to protect the generator from catastrophic engine failure if the oil were to get too low.

If the oil level on even ground is at the bare minimum to keep the sensor happy, then the engine will still run. However, if you tilt the RV even 5 or 10 degrees by parking it on uneven ground and the oil drifts away from that sensor and instead exposes it to air, then the sensor will stop the engine from ever starting.

image showing how parking an RV at an angle can cause the oil to flow away from the low oil shutoff sensor and stop the generator's engine

The solution is simple as well for this problem.

In the case of an extreme angle, make sure to level out your generator.

If the oil is low, simply unscrew the oil dipstick and check your level. If it’s on the very bottom or below the acceptable range mark, then simply add oil through that same hole with a funnel until the level is correct on the dipstick.

Failure to Prime Your RV’s Generator Will Keep it from Starting

This is a mistake that can be common with new RV owners or those who aren’t used to being the ones who start up the generator.

On most models, you’ll have a start and stop switch in the interior of your RV as well as on the generator itself.

The “stop” side of the switch is not just to halt the engine — it’s also the way you prime the generator with fuel before you start it.

Image showing how to properly prime an RV generator by holding down the "stop" switch for 5-10 seconds.
Be sure to prime the generator by holding down the “Stop” side of the switch for 5-10 seconds. This may take several tries if you haven’t ran your generator in a long time. You should hear it priming when you push the button. If you don’t, check your battery and fuel pump.

If you just hit the start button, your generator will likely just keep cranking but it won’t actually start up because there may be no fuel in the carburetor to be brought into the combustion chamber.

You will need to hold down the “stop” switch for 5-10 seconds first. You will actually hear the fuel pump priming the generator.

Try priming and starting your generator at least 3 times if you haven’t started in a long time. If it’s just been a day or so, usually it will start with a single priming session.

If priming and starting the generator inside the RV isn’t working, be sure to try doing the same procedure on the generator’s switch itself to rule out the interior switch being bad.

A Weak or Dead Battery Won’t Start an RV Generator

You RV will likely have 2 batteries — a chassis battery and a home or auxiliary (AUX) battery. It will vary based on how and who set up your system, but one of them will be hooked up to also start your generator.

There’s no hard and fast rule to what open voltage your battery will need to be to start your generator. Your generator might require that your battery be at least 50%, or you may get a generator that will start with a nearly dead battery.

Image showing how a weak or dead battery will not turn the RV's generator over.

To put it in perspective, a fully charged 12-volt battery will read 12.6+ volts with a multimeter, and a dead battery will read 10.5-volts and below. A 50% battery will read around 12-volts even, and a battery at 10% will read about 11.3-volts.

If you go to start your generator and don’t even hear the engine trying to turn over, or you just hear clicking sounds, then you more than likely have a dead battery for the task at hand.

Stale Fuel in Your RV Tank Will Prevent RV Generator Startup

This is an unlikely scenario, especially if you use your generator and RV on at least a yearly basis, but if you have let untreated gasoline sit in your RV’s gas tank for years, then the problem is likely that your fuel has oxidized and gone stale. In other words, it’s no longer combustible.

Hopefully you will have room in the tank to add fresh fuel and let the RV engine run on idle for a long time to burn out the mix of stale and good fuel so that you can start over again.

Going forward, make sure to treat the fuel in your RV’s gas tank with Seafom (1oz per gallon) before storing it. I have personally tested and confirmed SeaFoam’s claim that it will keep gasoline good for up to at least 2 full years and highly recommend it.

Image showing how leaving untreated fuel in the gas tank for a long time will cause it to oxidize and not start the RV generator.

Be sure to at least run the generator for a few minutes to allow the SeaFoam to cycle through the generator.

Everyone has a different method of winterizing their generator when it comes to leaving fuel in the carburetor or draining it, so I’ll leave that up to you. If you’re going to leave fuel in it, make sure that it has been treated with SeaFoam so that it won’t oxidize and go stale over the winter.

A Mouse Nest Inside Your RV Generator Can Break Internal Parts

Having trouble starting your generator after winter and you’ve ruled out the reasons above and verified that the spark plugs are working?

This one is not really easy to check without full access to the top of your generator, but your RV’s generator may have become home to a mouse family and they likely build a nest all around the crankshaft near the flywheel. I’ve had it happen to me.

Unfortunately, the crankshaft has a plastic band around it with 2 plastic wings that stick out and rotate that control the ignition coil for the spark plugs.

Once you go to start it, the generator spins really fast and those plastic wings sheer off due to the packed debris of the mouse nest.

I have a full article here where I show to how check the generator to see if this is your problem.

Image showing a broken ignition rotor on an RV generator due to a mouse nest.
The ignition rotor that broke in 3 pieces (only 2 recovered) due to a mouse nest over the winter.
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Robert Van Nuck

Robert lives in central Michigan and enjoys running, woodworking, and fixing up small engines.

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