Onan Generator Troubleshooting – (Manual Codes + Solutions)

Uh oh!  You are boon docking in a remote location and all of a sudden your Onan generator starts not working properly.  Or maybe you’re at a campsite and the shore power has been interrupted.  What should you do?  Your Onan generator malfunctioning could be a simple or complex issue to fix – either way we can help you out!

Today, Onan RV generators are most often found in RVs with Cummins engines, as the Onan Corp became a fully owned subsidiary of Cummins Inc in 1992.  Effective in 2017, the brand was changed to reflect the Cummins name across the board.

Although well designed and built, like any other mechanical part, the Onan generator can develop issues over time.  RV non-portable generators (those permanently installed in an RV) should be run regularly to ensure that they work.  Regular generator maintenance will help the generator run smoothly, but most importantly it will identify any issues before you need it to power the RV.  Most Onan RV generator issues can be solved before calling in a professional mobile or dealer RV tech.

The generator can be in different places on an RV.  Most diesel operated RVs will have the generator mounted in a pull-out on the front, as the diesel motor is in the rear.  Gas RVs will have the generator mounted in a side compartment. 

If the Onan generator starts and then shuts down, there are several troubleshooting steps you can take to identify the issue.  Gas-powered unit owners should check the Onan generator troubleshooting manual.

Newer Onan diesel-powered RV generators have fault codes that will display on the unit. 

The diesel-powered Blink Code list includes many issues you may experience, but the common fault code 36 is an issue that can have several causes from low fuel to some serious mechanical issues.

In general, the following Do-it-Yourself steps may help you resolve your problem.  Check these before calling a professional.

What to do if My Onan Generator Starts then Shuts Down

onan generator

4 Things to check if your Onan Generator is not working properly

Check the Fuel Level

If the generator is installed in your RV, it most likely is already connected to the fuel source, either gas or diesel.  There will be a line from the motorhome fuel tank to the generator.  Often this line is not quite long enough to pull fuel through if the RV fuel tank is below one-quarter full.  This will cause the generator to stall as it has no fuel for operation.  Make sure your RV fuel tank is always filled above the quarter-tank level.

In gasoline models the issue can also be temperature related.  In very hot environments it can experience vapor lock, a condition that will cause the normal fuel supply to stop.  Inside the RV compartment in a hot climate, the temperature can rise to above 120 degrees Fahrenheit.

There are a few propane-powered generators that cold weather will affect.  In these the issue is fuel vaporization.

Another check would be to inspect the fuel line to make sure it is open and not pinched.

Check the Oil Level

If the fuel supply is sufficient but your generator still starts and stops, check the generator’s oil level.  Onan RV generators have a “low oil” shutoff that could cause a shutdown.   As oil warms it thins out and this may cause it to fall below the proper level. 

Check Plugs and Filters

The general rule of thumb for generator maintenance is to change the oil, plugs and filters every 100-150 hours of operation.  Check the fuel filter to make sure it is clean and allowing fuel to get to the generator.  Replacing spark plugs and filters, running carb cleaner through the system, replacing the voltage regulator slip rings, and checking the circuit breaker on the back of the unit are additional steps you can take.

Final Checks

Have you checked the circuit breaker?  There is typically one on the generator, as well as one within the RV.  Additionally, check the ground wire to make sure it is firmly attached at both ends.

Also, there is no sure way to escape and protect your RV from rodents and bugs.  These critters can be the source of issues by building nests or chewing through wires. 

Onan Generator Error Codes

inside onan 5500

Codes from the Onan Generator Troubleshooting Manual

Code 1Engine Over Temperature
Code 2Low Oil Pressure
Code 3Service Check
Code 4Over Crank
Code 12Over Voltage
Code 13Under Voltage
Code 14Over Frequency
Code 15Under Frequency
Code 19Governor Actuator Overload
Code 23Low Oil Pressure Cutoff Switch
Code 27Voltage Sense Error
Code 29High Battery Voltage
Code 31Overspeed
Code 32Low Cranking Speed
Code 35Control Card Failure
Code 36Engine Stopped
Code 37Invalid Generator Set Configuration
Code 38Over Current (Field Overload)
Code 41Generator Rotor
Code 42Processor
Code 43Processor Fault Code.
Code 45Speed Sense
Code 47Ignition
Code 48Generator Field Sense
Code 51Processor
Code 52Fuel Injector
Code 54MAT Sender
Code 56MAP Sender
Code 57Over Prime
Code 58Exhaust Gas Temperature Shutdown
Code 81Exhaust Gas Temperature Sensor Open
Code 82Exhaust Gas Temperature Shorted
Source: https://www.cummins.com/sites/default/files/rv-manuals/A046L053.pdf

More Helpful Onan Generator Troubleshooting Tips

Regular Operation

It is important to operate your generator at least once a month under load.  Consider your generator as needing exercise to stay healthy.  You should start the generator, let it run at idle for several minutes, then turn on various appliances to put a load on the generator for several more minutes.  This process is important in generator engines with carburetors as fuel can degrade over time and cause an accumulation of varnish which can lead to binding of the various parts of the engine.

Placing a load on the generator causes it to work at capacity.  This may include running the air-conditioner(s), microwave, and other smaller appliances at the same time.  Some experts recommend a minimum of 15-minutes, while others say 30-minutes to one-hour of operation under various load conditions.  Check your Onan generator troubleshooting manual for the specific recommendations for your generator. 

Before turning off the generator, turn off the appliances and allow the generator to idle and cool down.

Onan tech specs

How often should you change oil in Onan 5500 generator?

You should consult your generator’s owner’s manual for suggested manufacturer’s intervals for service.  Most gas and propane generators require oil and air filter changes every 100 to 150 hours, or once a year – whichever comes first.  Those engines with a built-in check valve may require a specific type of oil filter.

While you can typically use standard automotive oil in your generator, many manufacturers recommend synthetic oil.  Note that many warranty requirements state that professional maintenance at the suggested intervals be done for claims to be honored.

Onan generator troubleshooting from YouTube

Today’s Do-it-Yourselfers often turn to the plethora of self-help videos on the popular how-to channel, YouTube, like the video above.  There are a variety of videos providing step-by-step guidance in both simple and more complex fixes to your RV.  Just type in your issue and model to find the listings and choose a video from the options.

Onan Generator Professional repair

If you are not handy at Do-it-Yourself projects, you may want to find a mobile RV repair technician or make an appointment at the RV repair shop. 

Onan Generator Starts then Shuts Down

Onan generator troubleshooting FAQ

Where can I find the hours of use for my generator?

All generators in motorhomes are equipped with an hour meter.  Some have interior displays that can be viewed, others have the meter display on the unit.  Check your RV generator owner’s manual for specifics on your unit.

What is an error code 36 on an Onan generator?

A fault code 36 means that your Onan generator has stopped without a shutdown signal from the control board, i.e., you have not turned it off.  There can be many reasons for this type of error code from lack of fuel to a more serious mechanical problem. 

How do I reset my Onan generator?

Resetting the fault codes on your generator is simple.  Locate the primer button and hold it down for about 30-seconds.  Release the button and then start your generator.

How do you read codes on an Onan generator?

Finding the fault codes on the Onan generator is relatively easy once you remove the cover or access panel.  Find the primer button and press it quickly three times within five seconds.  The light above the button will blink in a series.  It will repeat for up to fifteen seconds.  Count the number of blinks as the first number.  It will then blink in a second series, and this will be the second number.  For example, if it blinks three times at first then six times during the second, your fault code will be 36.
Here is a good YouTube video that shows where to find and how to read Onan generator fault codes.

Why won’t my Onan generator start?

Usually, the reasons why an Onan generator in motorhomes doesn’t start are easily fixed.  Here are the most common causes of the generator not starting.

1) The fuel level in the RV fuel tank is below one-quarter full.  Often the fuel line from the RV fuel tank to the generator is placed so that the generator does not deplete the RV’s fuel supply.  Maintaining a full fuel supply will prevent the generator from stopping.

2) A low oil level will prevent the Onan generator from working.  Most newer generators in diesel RVs have an oil-sensor that will turn the generator off when the pressure falls below a certain level.  Make sure the oil level is full by checking the oil dipstick and adding the recommended oil if needed.

3) Filters can become clogged and block fuel or oil from getting to the generator engine.  Make sure the filters are clean and free of debris by changing them at the manufacturer’s recommended intervals.

4) Plugs should be changed and carburetor maintenance done at the recommended manufacturer’s intervals of 100-150 hours of operation to ensure that the generator is operating at peak performance.

5) Check for loose or crimped wiring to the generator. 

6) Check the RV battery.  To start, the generator needs adequate battery power.

About Chad & Rick

Chad and Rick are the father son team behind Generator Hero. Rick is an engineer and manager, he’s used generators his whole life and specializes in fact checking our articles. Chad is a writer and webmaster helping to keep things running smoothly on the site. Read more about Rick and Chad, or send a message using this contact form.

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