How to Fix Fault Code 13 on Onan Generator? (Error Solved!)

onan generator code 13

The fault code 13 on the Onan generator is not the most common one that you can be facing, but as with all other error codes they more of an indication what was the state of the generator that led to shutting down, than a precise indication of what issue caused it.

This makes identifying the exact cause of fault code 13 a little bit inconvenient, as the problem which can lead to it can happen in many places.

Properly identifying and removing this issue is the precondition to having the generator working properly and reliably when it is needed, especially if you are planning on dry camping, away from the convenience of the shore power.

So, how to fix fault code 13 on Onan generator? To solve the error code 13 on Onan generator, just check and follow the steps below:

–           Step #1: Turn off the breakers

–           Step #2: Check the governor rod

–           Step #3: Turn on the generator breaker

–           Step #4: Turn on the main RV breaker

–           Step #5: Check individual appliances for shorting

Keep on reading to find out which of these issues you will be able to fix yourself, and for which you will have to take your RV to a dealership or a Cummins repair shop.

What is Fault Code 13 on Onan Generator

There are several causes that may lead to a generator producing less than 108 volts of alternating current.

Going over the details of all of them is beyond the scope of this article, and for some of them, you will not be able to diagnose yourself due to a lack of tools.

For example, you will not be able to measure the main winding voltages without the break-out tool 420-0603.

But, there are some common issues that you actually can both diagnose and repair.

A word of warning, before you start any work on your generator it is a smart thing to first consult your RV warranty policy and generator’s warranty policy.

Some work can void it if either of them is still in the warranty period, so it’s best to consult the policies of your RV dealership if you want to preserve the warranty on them.

Read also:

>> How to Fix Fault Code 12 on Onan Generator?

>> How to Fix Fault Code 14 on Onan Generator?

Reading the Fault Code on Onan Generator

Before you attempt to troubleshoot the cause of any problem, you need to establish that an issue exists.

Chances are that you are already certain that you are dealing with the fault code 13, but none the less it doesn’t hurt to go through the procedure of reading the code once more.

The Onan generators have a very simple way of signaling the fault code in case of some problem that leads to the generator’s shut down.

On the STOP/PRIME button, there is an indicator light that will blink in a specific pattern signaling the exact fault code.

  • The first thing you need to do is to press the STOP/PRIME button three times within five seconds.
  • This will initiate to display the fault code 3 by blinking three times in series and then making a pause. This code means that the shutdown was caused by a two-digit code.
  • Now, you will need to press the STOP/PRIME button once more, for around a second.
  • The indicator light will now start blinking the pattern specific to the fault code. There will be two groups of flashes, the first one specifying the first digit, and the second group specifying the second digit of the code.

Once the generator displays both groups of flashes, the indicator light will make a longer pause than the one between groups, and then start repeating the pattern.

It will continue repeating it for five minutes or until you press the STOP/PRIME button twice.

In case that the indicator light flashes once, then pauses, and then three times, you are dealing with the fault code 13.

Butt, in the case that it flashes some other pattern you are dealing with some other fault code, for which you can find instructions on how to deal with it on our blog.

Also, you should be careful not to mistaken fault code 31 for fault code 13, as that is a completely different problem, and trying to troubleshoot for a wrong fault code will only lead to wasting your time and nerves.

Troubleshooting fault code 13

The fault code 13 means that the generator is unable to produce the voltage required.

In a normal situation, as you are increasing the load, the voltage drops by a bit and the generator corrects for it.

The fault code 13 means that the generator wasn’t able to do so for some reason, so the place where you should start troubleshooting is the load.

So, the simplest thing is to calculate the overall load of all of the appliances and compare it with the generator’s capacity while making sure to take into account that with every thousand feet of altitude it loses around 3.5% of maximum power.

If that’s too complicated, you can simply turn off one of the ACs and restart the generator, if the problem is overloaded generator by appliances, whether it is exacerbated by the altitude or not, the problem should go away.

Step #1: Turn off the breakers

The first step is to turn all of the breakers and thus completely isolate the generator from any load.

You should turn off the breakers on the generator, main RV breaker, and all branch breakers.

“With all breakers off, you should start the generator and let it run for at least 20 minutes.”

If the generator stops and again shows the fault code 13, there are problems either with the control board, the alternator end of the generator, or with the governor.

If it doesn’t stop running, you should move to step #3.

Step #2: Check the governor rod

Very often when under load the generator is unable to produce a proper voltage because the governor rod spring is not properly attached.

On many models, it is located between the carburetor and the oil dipstick, where you will find a teethed and slotted bar to which it is supposed to be connected.

It’s supposed to be connected to the fifth slot when counting from the right side.

In case that it is properly attached, there still can be some issues with it, but the RV should be taken into the shop for more thorough diagnosing.

Step #3: Turn on the generator breaker

You should turn the AC circuit breaker on and leave the generator to be working for about 20 minutes.

In case that the generator stops and shows again the fault code 13, there is a short somewhere after the generator but before RV’s main breaker.

Potential culprits are the faulty transfer switch or the wiring leading to it.

In case that your RV doesn’t have the automatic transfer switch, but instead the generator is manually plugged in a receptacle, it could be shorting, so you should check it for any signs of damage caused by heat, melting, or charring.

Whether the problem is wires that carry the electricity to the transfer switch you will have to inspect visually, and how easy it is, depends on the model of your RV, but very likely you will need to get under it.

Damage to these wires is very often done by critters, and if your RV has sat for a couple of months unused, they very likely have nibbled one of them and it is shorting with RV chassis.

Step #4: Turn on the main RV breaker

 If the fault code doesn’t show up and the generator continues to work for 20 minutes, you should turn on the main RV breaker and leave the generator working for another 20 minutes.

In case that fault code 13 reappears, there is a short inside the breakers panel, between the main and branch breakers.

In case that there are no fault codes for 20 minutes, then the short is somewhere down the line and you should start troubleshooting appliances.

Step #5: Check individual appliances for shorting

Quest way to troubleshoot appliances whether some of them is shorting is to split them into groups the way they are wired to the breakers board.

So, you should be turning on one at a time branch breaker, start the generator, and then turn on all the appliances on that circuit, and let them run for 20 minutes.

If in any of these groups is a faulty appliance that is shorting, it will overload the generator and cause a drop of the AC voltage below 108V that will cause the generator to shut down with the fault code 13.

Causes of the Fault Code 13 You Can’t Fix

In case that the above troubleshooting doesn’t produce a fix for the generator’s shutting down with the fault code 13, chances are that the problem is with the generator’s alternator, either misaligned brushes or shorted windings, but most likely the problem is a faulty control board.

Neither of these issues is easy to diagnose or fix by the user, and the best course of action is to take the RV either to the dealership, to a Cummins approved repair shop, or to a repair shop of your choosing.

Prevent Fault Code 13 from Reoccurring

When it comes to causes of the error code 13 that are not related to the generator itself, you realistically can prevent only critters to nibble on the harness between the generator and the rest of the RV’s electrical systems.

But, when it comes to problems with the generator, mainly the slip rings and brushes, the only thing you can do is to anticipate the potential problems with them by having them inspected every 150 work hours, instead of the recommended 500 hours.

While Cummins’ representatives and technicians will assure you that these are very rare issues, truth is that newer Onan generators are a mixed bag when it comes to their quality.

Most Common ONAN RV Generator Problem

Today we look at the most common ONAN Generator problem… it will run as long as you hold the start button.

Fortunately, this problem is usually due to not operating the generator for a while. If your RV has been in storage for months or the generator hasn’t been started in years, most likely you have gummed up oil clogging your oil pressure switch.

I’ll show you how to diagnose and repair the issue in 5 minutes! Below are some additional helpful links for troubleshooting your ONAN RV generators.

Most Common ONAN RV Generator Problem Repaired in 5 Minutes! >> Check out the video below:


Mike Gilmour

Hi, I'm Mike, co-founder, and editor of RV and Playa. My passion is traveling (with my RV) and enjoying the day at the beach (Playa)! Well, I originally created this blog as a way to share what I've learned by experimenting with the RV lifestyle, and I want to help others develop in life through new skills and opportunities.

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