Fixing Onan Generator Fault Code 33 (What Does It Mean?)

Blink and pause. It is a simple way to communicate with the owner of the generator. But the message will not be received if the owner does not understand the blink and pause system. Also, the message won’t be received when the code is missing from the error code lists.

Believe it or not, some Onan error code lists skip this number and go from #32 to #35. That can be a problem when you see the 33 error code flashing. All this code means is that there is an overheating problem with your generator.

To learn more about this code, what it means and how to fix it just continue to read our article. it has the information you need to make the correct diagnosis. Even if that number is missing from error code lists.

Onan Generator Code 33 Causes


This code seems to be missing from the manual as well. The reason for that omission is that the problem is an uncontrolled shutdown. That shut down occurs when the generator is overheating.

When the Onan generator starts to get hot, the machine will turn itself off and flash a code that no-one knows anything about unless you go to an Onan-approved mechanic.

One of the causes for this code is that the overheat sensor may be malfunctioning. If it is, then you may have a hard time replacing it as corrosion is known to freeze the sensor in place and you may have to remove the engine head to get to it.

Another cause would be low oil. If that is the case, then all you would need to do is add a little more oil to the oil reservoir. Finally, two wires are going from the carb to a shut off which houses a needle and an electromagnet.

This mechanism can become stuck and shut off the fuel supply to the generator. Replacing it may be your only solution.

Why is My Onan Generator Overheating?


There are several reasons why this would be happening. As you just read, if you are not checking the oil regularly then the generator is not being lubricated properly causing the heat to build up and the sensor to shut the motor down.

If your generator is built into your RV, there is usually a fuel supply line to help run the unit. Your RV may be low on gas which would interrupt the fuel supply and again, overheat your generator.

Or as we just explained, the device monitoring the fuel supply to the generator could be malfunctioning and shutting that supply off. Then, the ECM system which heats the glow plugs that help the engine to start, may not be heating those glow plugs.

When that happens all it is telling you is that the heat sensor is going bad and you will need to replace it. The major problem with replacing the heat sensor is corrosion. Once it starts to take place, it can ‘weld’ the sensor to the engine making it extremely difficult to remove.

You may need to use those products like WD-40, Deep Creep, and more to get those sensors unstuck.

Fixing Onan 7500 Quiet Diesel Generator Fault Code 33


This is a bit difficult to get done as first, there is a little confusion about what the blinking lights mean. Some people do confuse the 3 blinking lights as fault code #33. That would be a big mistake.

Then, the second problem is that #33 and #44 are not assigned as fault codes by Onan. This makes troubleshooting a little bit more difficult. Fortunately, the #33 code seems to be the standard overheat warning for all Onan generators including this model.

You will find that if you stick your finger in the coolant that it may be barely warm. This means that there is another problem with the generator. The first place to look will be all the hoses to make sure there are no kinks, holes, and so on.

Then you need to move on to the oil and fuel supplies to make sure they are clear and full. After that, you will have to check the sensor. It may be bad and if you do not have the right tools to do this, you will need to go to an Onan-approved mechanic to get it checked.

If the unit is truly overheating, then just shut it down and let the generator cool off for a while.

Onan Generator Fault Code 33 Advice


The first piece of advice that should be given to every Onan owner is that you need to make sure to remove all loads before shutting the generator down. If you don’t you could damage the inverter and create an expensive repair.

Next, you need to be aware that the last blinking fault code will continue to blink for a time even after the problem has been corrected. That seems to be normal for Onan generators.

If you are not sure what all the fault codes mean or have lost the owner’s manual, etc., then click on Onan Generator fault codes. It will take you to the list of fault codes and have instructions on what they mean and how to fix them.

Notice that #33 is not listed there nor is #44. Other advice would be to place your Onan owner’s manual in a safe place, a spot you won’t forget about, and refer to that first. Especially if the unit is still under warranty.

Some Final Words

Proper communication is essential when you have a mechanical failure. Unfortunately, error codes are not always using the best method to communicate what is wrong. When you do not understand the code, have a list of codes ready to help you. If that doesn’t work, there is always a trusted mechanic waiting to help.

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