How To Read Onan Generator Fault Codes (Cummins Blink Code)

Has your Onan generator started blinking and you don’t know why? Perhaps there is something wrong with your generator but you don’t know what each fault code means? Or maybe you are curious and want to know more? Whatever your reason might be, we have the answer for you!

We know how difficult it can be to know what is wrong with your generator, especially an Onan generator. It sends the code out so quickly, that you can blink and miss it entirely! And that leaves you wondering what the code could be and what the problem is.

Even when we do catch the code, many of us are confused and unsure what it means. We search everywhere for the answers and come up empty-handed, doomed to never know the problem with our generator and how to fix it.

Well, no more! Today we are here with the answers that you need. Keep reading to find out what the Onan fault codes are, what they mean, and everything else that you need to know about them!

Keep your eyes peeled to become a generator expert and to know what each blink means!

How To Read Onan Generator Fault Codes (Cummins Blink Code)

Onan Generator Faults

When there is a fault with your Onan generator, it will blink to let you know. Each fault has a different code, using a different number of flashes or pauses to indicate the problem.

Now some of these can be quick and hard to spot, whereas others are easier to identify. Either way, it can be confusing if this is your first Onan generator, or you have never had a fault before.

But to help you decipher the code, we have a list of the different faults, what their code is, and what you can do to fix it! So let’s get into the article and solve your problems today!

Remember, if you have a problem with your generator and the code isn’t on the list, or you are having any issues that aren’t listed today, it is best to contact a professional to have them inspect the generator.

You want everything to be working smoothly to prevent an accident, so it’s worth spending the money and having it checked over, just to be safe.

Let’s dive in and take a look at some of these codes!

Low Oil Pressure (Code 2)

First up, we have low oil pressure. This code is a pretty easy one to spot as the light will blink twice. Once you see this code, you will need to add more oil to your generator.

To do this, twist the yellow cap to remove it and check the gauge. There you can see how much more oil needs to be added and you can fill it up to stop the flashing. When doing so, remember not to overfill your oil tank as this can cause more problems down the line.

Service Check (Code 3)

If you see three flashes, a pause, another three flashes, a pause, and three flashes continuing in this pattern, then it’s time for a service check.

This code means there is a problem with your generator that needs to be checked. You won’t be able to miss this code, as it continues to flash three times, pause, and flash again until you press the button.

Then, it will give you a secondary code. This code will tell you what the problem is with the generator so that you can make the necessary repairs or contact a specialist to do them for you.

If you aren’t very familiar with generators, we always think it’s best to spend the money and have a professional do the work. That way you know it’s done correctly, and it saves you a lot of stress!

Let’s take a look at what some of those secondary codes would be. Here we have numbered each code so that when you see the number, you know what it means and what to do!

Over Crank (Code 4)

When you see an over-crank code, the first thing you need to do is reset the control board. To do this, turn the switch off and press the reset button.

If you can’t find these controls, then be sure to check your user manual for a detailed diagram, or search for the generator online to find a downloadable version.

Once you have pressed the reset button, turn the switch back on. If the generator runs, then you are in the clear. If the code returns, then sadly, it is time for a new control board.

You can purchase these online usually, or you can visit your nearest electrical or hardware store to see if they have any in stock.

Over Voltage (Code 12)

Overvoltage is caused by a faulty inverter that overcharges the generator. This can be quite dangerous, and the only safe way to fix this is to take the generator to a repair shop or Onan dealer.

Now, this code doesn’t always mean that a faulty inverter is a problem. It could be a clogged filter or not enough fuel. It’s always worth cleaning or replacing the filter and adding more fuel to see if that helps before visiting a repair shop.

Related: Why it’s a bad idea to leave your inverter on.

Under Voltage (Code 13)

If you see this code, then your controller is unable to maintain the correct voltage levels.

Thankfully, under-voltage comes with an easy fix! Just unplug all appliances that you don’t need and leave the air conditioner and battery charger to run. This should help the generator restore its correct voltage levels.

This issue can also be caused by the engine slowing down. Several reasons can cause this, such as a lack of fuel. If you can identify the cause and avoid it happening again, you should not experience under-voltage again.

Over Frequency (Code 14)

An over-frequency code is generated when your engine is running too fast. There are a few things that could be causing this, like a broken governor, linkages not installed correctly, a misadjusted governor, carb issues, or an air leak in the intake.

To fix this issue, you will want to check your frequency levels first. You can then move to fix or replace the cause of the over frequency, by cleaning or replacing your carb, checking that the linkage is not reversed, or replacing the governor.

If you are unsure how to fix over frequency, there are plenty of tutorials online that can walk you through the process. Or you can take your generator to a dealer or repair shop to see if they can fix the issue. Often.

Over frequency is a fixable issue and providing that you keep your generator well maintained, can be avoided in the future.

Under Frequency (Code 15)

You guessed it, under frequency is the opposite of over frequency! This code shows that your engine isn’t running fast enough, which can be caused by things not being connected correctly, or the governor being in the wrong spot.

To check if yours is in the wrong spot, your governor needs to be in the 5th notch from the right. Make adjustments here if needed and check the generator again.

If it is still flashing, then you might have restarted your generator in less than a minute, and are now running in ERO mode. This will allow the engine to run but will offer no power.

To avoid this, turn the generator off for at least two minutes before restarting the generator and trying again.

Governor Actuator Overload (Code 19)

If your governor has not been installed correctly, then it can cause you problems. It should have one wire connected to the controller and one wire connected to the ground.

If one of these is loose, then it can trigger the governor actuator overload code and you will need to adjust the wires.

To do this, check both wires to see which one is loose. Simply tighten the wire and the code should vanish! If not, or the wires seem tight, then it is best to take the generator to a repair shop.

According to the manual, the generator should be taken to a certified Onan repair shop where they can identify the problem and repair it for you.

If you ever have any doubt or are unsure about a code or fault, be sure to check the manual first! It is packed with advice and explanations for the codes that can help you repair parts of the generator yourself.

If you do not have your manual to hand, search for it online and download a copy to keep safe.

Low Oil Pressure Cutoff Switch (Code 23)

If you see this code, then there is a problem with your cutoff switch. If there is a malfunction with the switch, then it’s a job for the professionals, not yourself!

The last thing you want to do is any more damage to the generator, or hurt yourself fiddling with wires and controls.

Instead, take our advice (and the advice of the manual) and take your generator to your nearest Onan dealer. They can identify and solve the problem for you, saving you the stress.

Throughout this article, there will be times when we recommend that you take the generator to an expert.

While this can be expensive depending on the fault, it is better to do this than hurt yourself or damage the generator attempting to carry out repairs yourself.

Voltage Sense Error (Code 27)

Code 27 suggests that your controller can’t sense the output voltage. This fault is another one best left to the professionals.

If you check your manual, you will see that Onan suggests you take it to an authorized dealer so that they can carry out the repairs for you.

Remember, if you don’t heed the advice in the manual and carry out the repairs yourself, you can risk voiding any warranty that you currently have, leaving you out of pocket!

High Battery Voltage (Code 29)

If you see the high battery voltage code, then the voltage across your battery system is over 19 volts.

Here, you will want to check the connections in your battery bank, you might need to reconnect them if they are not in the correct order.

You should have your 12 volt connections parallel and 24-volt connections in a series. You can check your user manual for some extra guidance here to make sure that you have done this correctly.

You can also set a lower battery booster charge rate to avoid the battery voltage getting too high again.

Overspeed (Code 31)

If you see three flashes, a pause, and one final flash, then your generator is going faster than 3,400rpm.

Now, this code can look a little similar to number 13, so to avoid confusion, press the stop button three times. You will want to do this in 5 seconds, so be sure to be quick!

Once done, you will return to the first three flashes. Press the stop button again and you will get a secondary code. Use this to double-check your reading and confirm if the code is 13 or 31.

If it is number 31, then you need to take the generator to a dealer for them to carry out the repairs for you.

Low Cranking Speed (Code 32)

You will get a low cranking speed code if your cranking speed is less than 180 RPMs for two seconds.

You can fix this by cleaning the battery connections, or charging and replacing the batteries. Changing the engine oil to one with the correct viscosity can also help with this problem.

Control Card Failure (Code 35)

Usually, this code appears during a self-test, and it’s the generator’s way of telling you there is an issue with the microprocessors EEPROM.

Again, this is another issue that is best left to the professionals, so be sure to take the generator to an Onan dealer nearby.

Engine Stopped (Code 36)

If the engine stops suddenly, then you could have run out of fuel, have a pressure issue, or issues with your spark plugs and leads.

You might also need to replace or clean your air cleaner, or there could be another mechanical failure causing the engine to stop.

You should explore every avenue, seeing if you can repair the generator yourself before seeking professional help.

Invalid Generator Set Configuration (Code 37)

This code informs you that your generator is set to the wrong frequency. To fix this, take your generator to your nearest Onan dealer, where they can rectify the issue with the correct tools.

Over Current Field Overload (Code 38)

This happens when your controller can’t sense the output voltage or field voltage. It’s best to take your generator to a professional to have them carry out the necessary repairs.

Processor (Code 42)

Code 42 tells you that there is an error in the generator’s Microprocessor Rom. Again, this is an issue best left to the professionals so that they can carry out the correct repairs.

Processor Fault Code (Code 43)

This code means there is a problem with the Microprocessor’s RAM, and you should follow the advice for the above error again.

Speed Sense (Code 45)

A speed sense code means that your controller cannot sense the quadrature frequency. You will want to let a professional look at the generator and carry out the repairs for you.

Ignition (Code 47)

This is another issue caused by the controller, and it cannot sense the ignition when you try to start the engine. This issue is best left to a professional to repair.

Generator Field Sense (Code 48)

Yes, you guessed it, another issue caused by the controller! This time, it can’t sense the field voltage in your generator’s operating system. Take your generator to an Onan dealer to have them fix the problem.

Processor (Code 51)

This is another code telling you there is an issue with your microprocessor. Once again, this is a job best left to the professionals, so be sure to take your generator to a dealer.

Fuel Injector (Code 52)

Code 52 relates to an open or short circuit in your fuel injector. Take your generator to an Onan dealer to have this repaired.

MAT Sender (Code 54)

If your MAT sender has an open or short circuit, chances are you won’t be able to fix this yourself. Once again, this is a job left to the professionals.

MAP Sender (Code 56)

It might look similar, but this is a different code from your MAT sender. Although, the problem is usually caused by an open or short circuit, only this time in your MAP sender. Leave this job to the professionals and take your generator in for repairs.

Over Prime (Code 57)

If your prime mode is longer than 3 minutes, then you will get error code 57. Remove any object that might be keeping the control switch in prime position and this code should vanish.

Exhaust Gas Temperature Shutdown (Code 58)

A restricted exhaust system, bad ignition, bad heat sensors, a lean fuel supply, and other issues can cause this code to appear. You will want to get your generator to a dealer for repairs here and to keep your warranty intact!

Exhaust Gas Temperature Sensor Open (Code 81)

This can be caused by a temperature sensor getting stuck open and not closing. Leave this one to the professionals and have an Onan dealer repair the issue for you.

Exhaust Gas Temperature Shorted (Code 82)

This can be caused by a short circuit and is best rectified by your local Onan dealer. They will have the tools on hand and can fix this without voiding any warranties.

Resetting Your Generator

Once you think the issue has been resolved, you might want to reset your generator to stop the code flashing. You can do this easily, following our three steps below:

  1. Find the primer button.
  2. Hold the button down for 30 seconds. Next, release the button and start the generator.
  3. Leave the generator running for 15 minutes. If the code does not clear then take it to a repair shop for an expert to look at it.

It really is that easy! Don’t forget to make use of your user manual if you run into any issues along the way!

Final Thoughts

And there you have it, a list of possible faults that your generator could have and how to fix them!

Now that you understand your Onan fault codes, you should be able to identify the problem easily and either fix it yourself or take it to your nearest authorized Onan dealer to carry out the repairs for you.

Be sure that you make use of these dealers to ensure that all repairs are carried out correctly and that your warranty remains intact!

Madeline Cooper