How to Fix Fault Code 29 on Onan Generator? (Error Solved!)

The fault code 29 is usually caused by an accident or by some serious issues with the wiring of an Onan generator in the RV.

It can be caused by few different problems but fixing the one which is causing the fault code 29 is a prerequisite to the generator functioning properly.

And properly working generator is the thing you will definitely need in case that you decide to take the RV away from the beaten tracks and far from the convenience of RV camping ground power connectors.

So, how to fix fault code 29 on the Onan generator? To solve the fault code 29 on Onan generator, just check and follow the steps below:

– Step #1: Inspect the batteries

– Step #2: Check the remote switch wiring

– Step #3: Check the battery voltage on the leads

– Step #4: Check the voltage of the batteries

– Step #5: It’s control board

The joy of it is in being self-sufficient, so keep on reading to find out how to diagnose the cause of the fault code 29, and how to fix some of the potential problems that are leading to this situation.

Table of Contents

What is Fault Code 29 on Onan Generator

When camping with an RV away from the beaten tracks, you are relying on your generator to provide you with electricity when you need it for powering all of the appliances inside your RV.

Because the generator is that important when it begins refusing to properly start and instead shows a fault code can be extremely alarming, especially if it is the fault code 29 which can be very tricky to diagnose and fix.

In the simplest terms, fault code 29 means that the batteries that the generator is using for the startup provide more than 19 volts.

There are several ways in which a generator’s control unit can end up detecting a voltage higher than 19V, and I will cover them later.

For starters, let’s cover how you can precisely determine that it actually is the fault code 19.

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Reading the Fault Code on Onan Generator

Before you start fixing or troubleshoot a problem you need to identify it and its symptoms.

Onan generators come with a very simple system for identifying general reasons for malfunctioning, the control switch has a built-in indicator light that blinks a certain pattern depending on the exact fault code.

Once some problem arises, it will keep repeating the specific pattern for five minutes, after which it will stop.

Thankfully, there are no reasons for worry, as you can easily retrieve this code at any time.

The very first thing to do is to press the STOP/PRIME button trice. You have five seconds for the 2nd and 3rd press after the 1st one, so there is no reason to hurry or frantically mash the button.
The indicator light will start blinking most likely a pattern of three flashes and one pause, over and over again. This is normal, it is the fault code 3 which means that you will need to perform actions needed for reading out the two-digit fault code, which is what you are trying to do.
Next, you need to make a long press of the START/PRIME button, it should last for about a second.
Once you depress the button, the blinking pattern will change. There will be two groups of flashes separated by a short pause, and after the second group will come a long pause. The first group is the first digit of the fault code and the second group is for the second digit of the code.

If you see that the indicator light first flashes twice and after a short pause it flashes nine times, it means that you are dealing with the fault code 29.

If you are not certain whether there were 8 or 9 flashes in the second group, it is not a problem.

“After the second group of flashes, there is a long pause after which the blinking pattern will repeat, and it will cycle that way for five minutes, so you have enough time to make sure it is the fault code 29.”

If you are seeing a different pattern, you will need to consult the owner’s manual for the identification of that fault code.

For example, if there were 3 flashes in the first group or 8 flashes in the second group, those are completely different fault codes that require completely different solutions.

Once you are certain it is the fault code 29, you can either leave it be, as it will stop blinking after 5 minutes, or press the START/PRIME button quickly twice, which will make it stop.

Troubleshooting Fault Code 29

There are several reasons why fault code 29 may arise, some of them require the replacement of parts, but many are somewhat easy to identify and fix.

Some issues are considered as being outside the ability of a user to properly fix them, and attempting to do so can void your warranty.

So, it is a prudent thing to first check the conditions of your warranty with your dealership rep before starting any work.

Granted, in case that your generator is out of the warranty period, you may still want to be careful not to just aggravate the problems you already have.

If you are uncertain of your own skills, it’s always better to leave fixing the problem to experienced professional technicians.

Check first for the simplest solutions

Very often, especially with RVs that have dual inverter systems, which can both supply the alternating current from your deep cycle batteries but also work as a converter and charge them from the shore power or generator, fault code 29 can show up because the batteries are not set to charging.

So, fixing this problem can boil down to just flipping the switch on your inverter.

Another very simple fix is in a situation that your RV has a battery disconnect switch, it’s maybe turned off but the generator needs the power from batteries so it would start.

If it was installed by an RV dealership, you can find its location in the user manual for your RV and simply turn your batteries on.

If this doesn’t fix your problem, you will need to troubleshoot why the generator is getting or thinks that it is getting more than 19V when trying to start.

Step #1: Inspect the batteries

In case that your RV has a set of batteries instead of a single one, and you have replaced them recently, there is a chance that they are wired back in series instead of parallel.

Checking for this boils down to visually inspecting the connections between them, in a parallel connection the positive terminal of one battery will be connected to the positive terminal of the second one, the same will be with negative terminals.

In serial mode, the positive terminal of one battery will be connected to the negative terminal of the second one.

Step #2: Check the remote switch wiring

If the batteries are wired properly or you have only one, you should check the wiring of the remote switch.

While it sounds complicated, it is actually very simple, just outside of the generator housing on its right side is the 8-pin P1 connector of the remote switch.

You should disconnect it and then try to start the generator, if it starts it means that there is a short in the remote switch, and the whole harness needs to be replaced, which can be done only in a professional shop.

Step #3: Check the battery voltage on the leads

For this troubleshooting step, you will need a multimeter so you would be able to measure the voltage on battery leads.

First, you will need to disconnect the battery leads from the generator, and then measure the voltage on the leads.

If you measure the voltage above 13V, it is very likely that there is a problem with battery wiring and that they are shorting, but there is one more thing to do.

Step #4: Check the voltage of the batteries

You should also measure the battery voltage at terminals, so first, you need to unclamp the wires from them.

In case that you have two or more batteries, there is no need to disconnect all of the wires, only the two that are going to RV, one is connected to the positive terminal of the first battery in the bank, and the other to the negative terminal of the last battery in the bank.

Once disconnected you should measure the voltage on terminals, and it doesn’t matter whether you will measure on terminals of different batteries, for example, those two from which you have removed wires going into RV, or on the same battery.

As long as you put one probe on a positive terminal and the other to a negative terminal you are safe and will get the proper reading which should be 12.6V if your batteries are full, or a lower one.

The fact that these two voltages are different should tell you that there is some problem in the wiring and it needs to be replaced in the professional shop.

Step #5: It’s the control board

Well, if none of the above doesn’t work, it means that the control board is faulty and erroneously detecting the voltage, and needs replacement.

This is a straightforward thing to fix, and there are many aftermarket control boards that are higher quality than Onan’s OEM one, but if your generator still in warranty it will be voided.

To keep the warranty, you should take your RV to a dealership for them to replace it.

Prevent Fault Code 29 from Reoccurring

Fault code 29 occurs when the generator’s engine is receiving a too high voltage when trying to start or doesn’t receive any voltage at all.

The excessive voltage can be caused by three issues, RV batteries being connected in series instead of parallel, faulty remote switch harness, or faulty battery wiring.

Improperly connected batteries, if you have more than one, can be prevented by properly reconnecting them when you are changing them.

Damage to remote switch harness or battery wiring is usually caused by critters, so keeping them away from your RV is the only way to prevent this issue from arising again.

References

https://www.cummins.com/sites/default/files/rv-manuals/A035D009.pdf