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Motorhome Generator Troubleshooting: Get It Running!

Motorhome Generator Troubleshooting: Get It Running!

No matter where owners of motorhomes may roam, our generators are incredibly handy for running appliances like air conditioners, microwaves, heaters, and more. Even if you have a large solar and battery installation as we do… trees, clouds, and night happen.

But if your RV generator starts acting up, it’s time for some motorhome generator troubleshooting, and today’s post is a guide for just that.

Although there may be some tips here that apply to portable RV generators as well, this post is primarily about the onboard generators commonly found on motorhomes. Those are typically Onan brand or possibly a PowerTech.

What Is an RV Generator?

An RV generator typically comes in one of two forms. You’ll either have a built-in generator or a portable generator.

Again, this post is specifically geared to a motorhome’s built-in generator. But all RV generators, including portables, bring power to your RV in similar ways.

The purpose of a generator is to provide power/electricity to the appliances and other electrical equipment in and on your RV.

A built-in RV generator uses a circuit breaker panel to send electricity to your appliances and other electrical equipment. It also provides power to your rig’s converter/charger for the purpose of charging your RV’s batteries.

What Kind of Generators Are In Motorhomes?

A motorhome’s onboard generator is a built-in unit that generally takes its fuel from the motorhome’s fuel tank.

It’s also possible for an onboard RV generator to be fueled by the rig’s propane system, though this isn’t the most typical application.

Generally, a motorhome will have a built-in generator that is connected to the tank that fuels the engine. That same fuel tank will be set up to deliver fuel to the rig’s generator. So expect to find a diesel generator in a diesel motorhome, and a gasoline generator in a gas rig.

This is one reason it’s important to maintain sufficient fuel in your motorhome’s fuel tank. More on that in a minute.

The generators most commonly found in motorhomes are from Cummins-Onan. It’s also possible that your motorhome uses a built-in generator from PowerTech. However, Onan/Cummins-Onan is the most common brand of generator found to be built into all sizes and classes of motorhomes, both gas and diesel.

There are older RVs out there that may have a built-in Generac generator, but Generac is currently more a source of portable generators for RVs (and home or contractor generators).

Basic Motorhome Generator Troubleshooting

When you have a built-in motorhome generator, it’s important to know how to troubleshoot common issues to get it up and running again.

Let’s take a look at the most common problems that can crop up with motorhome generators and how to address them.

My Motorhome Generator Won’t Start, or Starts then Stalls

There are a number of issues that could cause an RV generator to fail to start or to fail to continue running.

Troubleshooting each of these could help you to isolate the cause and get it running well again.

Check Your Motorhome’s Fuel Level

If your generator simply stops, the first thing to do is make sure that your motorhome has more than 1/4 of a tank of fuel. Remember that most motorhome generators operate from the same fuel system as the motorhome engine.

In order for your RV’s generator to start, there needs to be sufficient fuel in your motorhome’s fuel tank. The fuel pick-up for the generator is almost always placed above the fuel tank’s low point.

This fail-safe design prevents you from running your rig’s fuel tank too low when you run your generator, causing you to run out of fuel and leaving you stranded.

Basically, it won’t allow you to use up all your fuel by running the generator. But that also means you can’t run your generator if the fuel gets too low in the tank. The exact level varies, but it’s a good bet that getting too far below 1/4 tank could lead to this happening.

When you’re troubleshooting any non-start issue or stalling issue, first confirm that you’ve got plenty of fuel in the tank. And fuel up before a big boondocking trip!

Check the Condition of Your Motorhome’s Coach Battery

If your generator won’t start from the control panel inside your RV, try starting it from the start switch on the generator itself. If it still won’t start,  check the condition of your batteries to be sure they aren’t drained.

If you press the generator start switch and you hear a clicking sound but the generator starter doesn’t turn over, then it’s possible that your coach batteries are nearly discharged.

You could also have a poor battery connection or a defective battery cable, or a failed starter solenoid. These can all be checked using a multimeter.

Check all of these potential issues before proceeding further. If you can rule out all of the above, then your clicking could indicate that the starter is bad.

Check Your Generator’s Oil Level

Another fail-safe mechanism that can be built into a motorhome generator is a low-oil shut-off. If the oil level in your generator falls below a certain level, the genny will fail to start (or will shut down).

Check the oil in your generator according to the directions in your owner’s manual, and if the oil is low, top it off and try restarting.

This may be a good time to mention that an important part of generator maintenance is to change the oil on a regular basis… that is, at least once a year.

Check the Main Circuit Breaker

Once you’ve confirmed that you have sufficient fuel in the shared tank and sufficient oil in the generator, you’ll want to confirm that your main circuit breaker isn’t tripped.

Sometimes an appliance such as a microwave or space heater can trip the main breaker. This can also occur as a result of a power surge or even a short circuit somewhere in the system.

Obviously, if it’s tripped you’ll want to reset it and then try again to start your genset.

Confirm that Fuel is Getting to the Carburetor

This applies to gasoline generators, since diesel models don’t have carburetors.

Having sufficient fuel in the engine’s fuel tank is only one piece of the fuel-related puzzle when troubleshooting an RV generator.

You also need to make sure the fuel is actually getting from the tank to the generator’s carburetor.

To do this, you’ll need to disconnect the fuel line going to the carburetor to ensure that there’s a steady flow of fuel. When you disconnect the line, be sure to have a bowl or bucket handy to catch the fuel, and try to start the engine.

If you’ve got a steady stream flowing, you’ve confirmed the flow of fuel. But if it’s dripping slowly, sufficient fuel may not be making its way to the generator’s carburetor.

You’ll also want to check the fuel filter and fuel pump to make sure that neither of these is obstructing a steady flow of fuel through the fuel line.

Our friend Brian of RV With Tito had his motorhome’s gasoline generator starting up just fine but shutting down after running for 15-20 minutes or so. The problem was the fuel pump. But as he was troubleshooting the issue, he created a great video showing exactly how to check all of these fuel-related items. We highly recommend watching it.

Check the Spark Plug

Again, this is a gas genny issue. Spark plugs can last for years in a well-maintained generator, but a bad spark plug can keep your genny from starting or running.

A bad spark plug is generally covered with carbon or even fuel or oil.

It’s not hard to pull a spark plug and check it or replace it, and it just might be the thing that’s keeping your generator from starting or running well.

If your generator’s spark plug is wet, it may indicate a problem that’s causing oil or fuel to wet the spark plug.

Your spark plug should be dry and a light brown/tan color.

Replacing the spark plug should be an easy and inexpensive job.

Check the Air Filter

If you watched the video above from our friend Brian above, you may have noticed that while he was servicing his motorhome’s generator he changed the air filter.

If your RV starts but does not stay running, it’s possible that a clogged air filter could be the problem. This is because generators run on the correct mixture of air and fuel, which is needed to keep the generator’s engine operating properly.

If the air filter is clogged, it won’t get the proper ratio of air to fuel. A generator’s air filter should be replaced as part of routine maintenance.

My Motorhome Generator Starts and Runs But There’s No Power to the RV

If your generator starts up just fine and is running well but isn’t bringing power into your RV, then you’ve got a different type of issue to troubleshoot.

Note that most modern RVs have generators that are hardwired to the RV but there may be some older RVs on the road that used a plug to connect the generator to the RV.

If you happen to have an older rig like this, you’ll want to check to confirm that the plug is in good shape and is securely in place.

Motorhomes and all RVs vibrate from driving which means that plugs, wires, and fittings can sometimes come loose.

Check Circuit Breakers and Fuses

The first step in troubleshooting the electrical side of your generator’s performance is to confirm that no circuit breakers are tripped and all fuses are good.

Remember that a circuit breaker can trip without completely snapping to the “off” side (they usually stick straight out when tripped). So, when you’re troubleshooting an electrical issue, you’ll want to manually flip breaker switches off and on for a thorough check.

As for fuses, you may have a fuse panel that is equipped with a light that comes on when a fuse blows. In this case, you’ll simply look for any light indicating a blown fuse.

If you don’t have this type of fuse panel, you can simply test your fuses with a multimeter or a test light, which is particularly easy to use for testing fuses.

Touch the probe to each of the metal pins on the face of the fuse. A good fuse will find both sides lighting your test light. If only one side of a fuse illuminates your test light, you’ve identified a bad fuse.

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To use a multimeter to check a fuse, simply set your multimeter to continuity and touch the probes to each side of the fuse. If you have continuity, then you’ve got a good fuse. If not, your fuse is bad.

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Note that most generators have a circuit breaker at the generator itself. If you or someone else has been working in your generator compartment, it’s possible that this circuit breaker was accidentally tripped, so be sure to check this breaker as well.

How Can I Prevent Motorhome Generator Problems?

The easiest way to ensure that your motorhome’s generator performs as well as possible is to be consistent with maintenance.

To help you with this process, here are a few of our videos illustrating how we maintain our Onan motorhome generator. When you conduct your annual maintenance, you can follow along with these videos to keep your generator functioning as well as possible.

We have one the most common diesel generators on the market: An Onan QuietDiesel. That’s what we used to demonstrate the various maintenance tasks in the video below.

How to Change the Oil, Replace the Air Filter, and Clean the Spark Arrestor

How to Replace Your RV Generator’s Fuel Filter

How to Change the Coolant in Your Onan Diesel RV Generator

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Richard Gorton

Friday 16th of June 2023

Excellent description on maintaining an Onan Jenny. I have an Onan Quiet Diesel 8500. Hopefully the components are in similar location.


Friday 16th of June 2023

Can't say 100% for sure, Richard... but the 8K generator was the evolution of the 7.5... so our guess is that most things will be very similar, if not downright the same.

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