How to Read Onan Generator Fault Codes?

Onan generators are some of the absolute best models you can get for use in an RV. However, like any machinery, they can have problems for no apparent reason.

With Onan, your generator sends out a code to tell you the problem. However, you could miss this if you don’t happen to be in the vicinity when the issue happens.

However, even if you see the Onan generator codes, it’s good to know what they mean and how to read Onan generator fault codes.

onan generator

It isn’t hard to read the Onan Fault Code blink system, although it is handy to have all the faults you could find and explain them.

Onan generators don’t display numbers; they blink. For instance, if the code were 41, it would blink 4 times, then pause and blink another once.

In our guide, you can learn all about the different codes for Onan generator faults, what they mean and what you can do to fix the issue. (Learn How to Ground a Generator When Camping)

How Do I Reset My Onan Generator?

If you don’t have your Onan generator troubleshooting manual, here are the steps you need to reset your generator.

  1. Locate the primer button on your generator. You will find it on the side of the unit, under the gas tank. It also acts as your start and stop button for your generator.
  2. Hold the prime button for a minimum of 30 seconds.
  3. Release the button and start your generator.
  4. Let your generator run for 15 minutes, and make sure the fault code has cleared. If the fault code remains, it means you may require further repair on your generator, so you’ll have to contact your Onan service dealer.

What Does It Mean When My Onan Generator Blinks 3 Times?

Should your Onan generator light blink 3 times in a row, it shows a service shutdown, and you will require secondary Onan generator troubleshooting codes from your generator.

Press the Prime button once to prompt a second, two-digit fault code.

The code comprises two sets of flashes. The light blinks a set number of times and will pause before it blinks the second number of times.

You will see a second pause following the second code as it will repeat. For example, a common error code 36 is 3 flashes, a pause, and 6 flashes. It will pause and repeat until action is taken. (Read Ways to Quiet a Generator)

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Why is My Onan Generator Light Blinking?

Here you can find all the codes with some associated details of what the error code means.

Code 2 – Low Oil Pressure

The code will blink twice only. It shows the generator has a low oil level. Pull off the yellow cap to check the oil gauge.

Code 3 – Service Check

You have an issue somewhere on your Onan generator. You see 3 flashes, a pause, 3 flashes, and repeats until you get the secondary code.

Code 4 – Over Crank

If you see this code, then try resetting your control board. Turn the switch off and hit the reset button. Turn the switch to run, and it should be fine. If the code comes back, you need a new control board.

Code 12 – Over Voltage

With this problem, you have a faulty inverter that overcharges the generator. To solve this, you need a qualified Onan dealer or repair shop. You can also the code because of lack of fuel or a clogged filter problem. Add fuel or replace the filter before you find a dealer.

Code 13 – Under Voltage

The controller is incapable of maintaining proper voltage levels. A simple fix is to unplug all appliances not used as the air conditioner and battery charger is running. A lack of fuel can also cause this.

Code 14 – Over Frequency

This code informs you the engine is running too fast. Sources of the code can be an intake air leak, carb problems or linkages not installed correctly, misadjusted governor, or broken governor.

Check the frequency levels first before you clean or replace your carb. Check the linkage isn’t reversed, or you can replace the governor. (Read Dometic Duo Therm Air Conditioner Troubleshooting)

Code 15 – Under Frequency

When you see this code, the motor is running too slow. The solution could be parts are not connected properly. If the generator still flashes, you could have restarted your generator in under a minute, and it has have run it in ERO mode.

In this engine running mode, you’ll find no power output. Turn off your generator, then wait for 2 minutes before restarting.

Code 19 – Governor Actuator Overload

The governor has a wire to the controller and another to the ground. If either is loose, it triggers the code. Check for loose wires and tighten.

Code 23 – Low Oil Pressure Cutoff Switch

This code would indicate a problem with the cutoff switch, which you can’t fix yourself.

Code 27 – Voltage Sense Error

The fault code here says the controller cannot sense the output voltage. Again, it would help if you had the expertise to repair.

Code 29 – High Battery Voltage

Such an error shows battery voltage is over 19 volts. Check your battery bank connections and reconnect.

Code 31 – Overspeed

3 flashes, a pause, and another flash mean your generator spins faster than 3,400 rpm.

Code 32 – Low Cranking Speed

Your cranking speed will be under 180 RPMs for 2 seconds. Clean your battery connections to fix.

Code 35 – Control Card Failure

The generator is informing itself there is an error in the microprocessor EEPROM.

Code 36 – Engine Stopped

You could run out of fuel or have low LPG pressure issues. It can also be spark plug leads are loose, or the plugs are bad.

Code 37 – Invalid Generator Set Configuration

The generator is set at the wrong frequency.

Code 38 – Over Current

You have too many devices that want power load from your generator etc.

Code 41 – Generator Rotor

The controller can’t sense either field or output voltage. Take to a Cummins Onan dealer for repair.

Code 42 – Processor

The Onan generator detected an error in its Microprocessor Rom section.

Code 43– Processor Fault Code.

There is a Microprocessor RAM problem.

Code 45 – Speed Sense

The controller is not sensing the quadrature frequency.

Code 47 – Ignition

The controller cannot sense any ignition to start your generator.

Code 48 – Generator Field Sense

The controller can’t sense an important part of the generator’s operating system.

Code 51 – Processor

This is another code for a problem with an installed microprocessor.

Code 52 – Fuel Injector

This will be an open or short circuit in your fuel injector.

Code 54 – MAT Sender

The MAT sender has an open or short circuit in it.

Code 56 – MAP Sender

This isn’t the same as the MAT, but pressing problems are the same.

Code 57 – Over Prime

When your prime mode is over 3 minutes, the error code appears. Check to make sure no object is holding the control switch in its prime position.

Code 58 – Exhaust Gas Temperature Shutdown

A lean fuel causes this error code. It can also be a restricted exhaust system, poor ignition system, faulty heat sensor, or other related problems a Cummins Onan dealer needs to fix.

Code 81 – Exhaust Gas Temperature Sensor Open

Here, it could mean the temperature sensor is stuck open.

Code 82 – Exhaust Gas Temperature Shorted

It may mean you have a short circuit, and you need an authorized Cummins Onan dealer to resolve the issue.

How to Read Onan Generator Fault Codes (2)

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