Troubleshooting an Onan 5500 Generator That Won’t Start

Even good pieces of equipment breakdown. This possibility happens to the best of them. If not Onan, then a Rolls Royce or a Cadillac. Even Rolex has trouble from time to time. It is the nature of this life to have to fix products that have a flaw somewhere in their system.

There are at least 15 good reasons why your Onan generator will not start. Anywhere from low oil to low fuel to a fuel leak to a bad ignition coil. You just have to take your pick and go through the list one by one until you solve the problem.

To learn more about this topic and how to fix those 15 reasons why your Onan won’t start, just continue to read our article. It has the information to help you out of a difficult situation. Take a few minutes to see how this important information helps you solve your Onan issues.

Onan 5500 Generator Troubleshooting

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This action depends on what is wrong. Each reason why your generator won’t start usually has its own repair process. For example, if the problem is low oil, you just need to add more oil. If it is low gas, then you add more fuel but you never exchange those fixes.

A bad fuel valve may need to be cleaned or replaced and replacement is often the same option for many parts that stop your Onan generator from starting. The key is to first identify the source of the problem and then choose the proper repair option.

Many times the parts are so bad, that replacing the part is the only way you can go. As usual, if you are not mechanically inclined or your Onan generator is still under warranty, let the professionals handle it.

That way you won’t cause more damage or void your warranty. keep yourself protected and know your limitations. It may be fun to work on motors but not everyone can do it well.

Onan 5500 Won't Start

Before you go to the list of reasons why your Oana won’t start, try to prime the machine first. If that does not work, then one of the following parts may be the source of the problem.

Here is the list of the 15 parts or reasons that keep your Onan generator from starting:

Low Oil

Low Fuel

Bad Fuel Valve

Clogged Carburetor

Bad Spark Plugs

Bad Oil Sensor

Dead Battery

Clogged Fuel Filter

Bad Ignition Coil

Faulty Recoil Starter

Bad Safety Switch

Faulty Fly Wheel Key

Bad Start Switch

Bad Voltage Regulator

Fuel Leak

It is a long list and by the time you get through it, you may have spent the whole day trying to fix the problem. The key is to go one by one to make sure you do not have to go through the complete list.

Maybe you will be lucky and hit the right part the first time out. If so you may want to start picking numbers for the lottery.

Why Does My Onan 5500 Generator Keep Shutting Off?


You can pick any number of those sources as the reason why your generator starts and then shuts off. Most of them will be the source at one time or another. We will pick just a few of them to explain why this takes place.

1. Low oil- this is the way they are designed to work. It is normal for the machine to shut itself off when it detects a low oil level. This is a protective device so you do not accidentally ruin your Onan 5500. Just make sure to check the oil regularly.

2. Low fuel- Again the generator is designed to shut itself off when it detects that the fuel level has gone below a quarter of a tank. It is a safety measure to protect you and the machine. Refilling the fuel tank is your only solution here and that is very easy to do.

3. Stale gas- Onan generators run off gas and not diesel fuel. If the gas has sat inside the tank for some time, it could get stale or go bad on you. When that happens the generator will not start. Replace the gas to get it working again.

4. A clogged carb- when this situation happens, the machine is not getting enough gas, or the air to gas ratio is bad. The source for the clog varies and can come from different sources. Clean the carb to solve this problem.

5. A clogged air filter- like the carb, the generator needs a good air supply to function correctly. If the air filter is clogged too little air is getting inside the engine and the generator will shut down. Clean or replace the air filter to stop this from happening.

Onan 5500 Will Not Stay Running

This problem may not be totally related to the above list of sources. One possible source for this could be the spark plugs. If they go bad, then it is hard for the generator to function. Simply clean, re-gap or replace the spark plug.

Next, the source could be the generator has overloaded. Modern technology has designed these machines to shut down when they are asked to deliver more power than they can. The best you can do here is to lighten the electrical load and re-start the generator.

You should also check the control board to see if it has gone bad or is flashing an error code that describes the problem. The machine may not be getting enough voltage either. Check to see if the generator is creating a magnetic field or not.

Again leave this type of work up to professionals if you do not have the right tools, skills, or knowledge of how the generator works.

How do I Reset My Onan 5500 Generator?

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The following information comes from the manual put out by Heartland:

To Reset Generator when code is set:

1. Turn off Breakers on Generator

2. On the Generator push STOP twice rapidly followed by one rapid push

to START. Do not start the generator.

3. Hold down Stop/Prime and it should show a steady red light. If not

repeat above.

If it has a steady red light on Stop/Prime then start the generator as usual. Once it stabilizes turn on the breakers.

To clear a fault code, push and hold the primer button for about 30 seconds. When that time period has passed, release the button and re-start the machine.

Then let the generator run for about 15 minutes to make sure the code has been cleared. Check the manual for your specific 5500 model and see what procedures you have to do. Not every generator is designed in the same way

Or ask a friend or mechanic that has experience in resetting the generator if these ways do not work.

Onan 5500 Altitude Adjustment

When you have questions about different situations involving your generator, you can go to the forums after reading our information. There is a lot of good advice out there that will help you solve your problems very quickly.

If you are not running the generator on your way up or on your way down to your destination, then you should wait to adjust the altitude levels when you arrive at your destination.

If you are going to run it while you travel, then you should adjust it before you leave your current area or stop and turn it on as you make your way. For the Onan 5500, there is a lever that you slide one way or the other.

This lever will help the generator get the fuel mixture it needs to perform up to expectations. There is a needle inside the jet orifice that is controlled by the lever and it makes the air to fuel mixture ratio match the altitude you are in.

You just have to move the lever one way to make the mixture leaner or the other way to make it richer. Check your owner’s manual to make sure you are moving the lever in the correct direction for your destination.

Onan 5500 Carburetor Adjustment


If the carb on this model is not sealed then there should be a bolt attached to a spring that will adjust the carb for you. You just have to trace the spring to this bolt. On the other side of the flange, there is a nut.

You turn the nut to adjust the carb. Which direction you go depends on the type of adjustment you need. The nut turned one way will increase your generator's speed and in the opposite direction will decrease that speed.

This system is just like adjusting a car or truck’s carb back in the day when your parents were young. The process to adjust the speed has you warming the generator up for 5 minutes and then placing a light to moderate load onto the machine.

Then turn the night until you hear the sound of the motor at the speed you are looking for. When you reach that spot, reduce the load and let the generator idle for 30 seconds. After that increase to a full load.

Now adjust the screw in the governor’s arm until the engine runs smoothly. keep adjusting the screw until the engine runs smoothly at full speed and at idle.

Onan 5500 Won't Prime

This could be due to the fact that no power is getting to the prime/start function. You may have to check the power supply with a multimeter. First, try the reset button located in a row of mini circuit breakers near the battery.

You may miss the reset button because it is not very large. Check all your power sources to make sure they are not the problem, a breaker did not trip, and so on.

Another issue that may cause this is a stuck primer switch. That part may need to be cleaned or replaced to get the prime function working again. Or the problem may lie with the remote feature. One or the other or both sides of the connection may be bad.

The best thing to do in this situation is to look at the troubleshooting section in the owner’s manual. It is supposed to be very detailed and should cover this problem. Or if you want you can talk to an Onan dealer or a good Onan mechanic.

They may have other ideas that will solve your issue.

Download Onan 5500 Generator Manual


It is easy to lose or misplace a manual. When you buy an RV or travel trailer, you are given a lot of them at one time. That is why this section exists. It leads you to several online manuals that you can download, save or print out.

It is always a good idea to save a copy on your computer and then print one out the next time you lose or misplace your current manual. That move should save you money.

Here is the first link and it may cost to download. At least you can view it for free. The second link is here. There are several versions on that website. The manufacturer is always a good place to go. You can see the manuals on the Cummins website support page.

These three links should get you on the right track and a quick search should turn up more options in case these do not work out for you.

Some Final Words

With such a long list of possible sources, it may take a while to find the actual problem. Do the simple fixes first that way you can save time and energy. Check the oil and gas tanks regularly so you can eliminate two possibilities before you get started.

When in doubt don’t be afraid to ask for help. That is what technicians are there for as well as dealers.

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