Onan Generator Only Runs When Holding the Start Button: Causes, Solutions, and Troubleshooting Guide

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Imagine the frustration of relying on your Onan generator during a power outage, only to discover that it will only run while the start button is held down. 

It’s a perplexing issue that many generator owners have encountered, leaving them puzzled and seeking answers and troubleshooting guides. 

The issue of an Onan generator only running when holding the start button can be attributed to various factors, including a faulty control board or relays, low battery voltage, a stuck or defective start button, wiring issues, low oil levels, lack of water in the radiator, insufficient fuel supply, or clogged filters.

Hence, in this blog post, we’ll talk more about these causes, explore the possible solutions, and provide you with a step-by-step troubleshooting process to help you get your Onan generator running smoothly once again.

Causes Onan Generator Only Runs When Holding the Start Button and Ways to Fix it

The start button on an Onan generator is designed to initiate the start-up process and activate the necessary parts of the generator to generate electricity. 

Typically, the button is pressed momentarily to engage the starter motor, which, in turn, initiates the engine’s combustion process. 

Once the engine starts running smoothly, the start button is released, and the generator continues to operate independently

However, in some cases, Onan generator owners may encounter an issue where the generator only runs while the start button is held down. 

This puzzling problem can leave individuals seeking answers and solutions to restore their generator’s normal operation.

Having said that, let’s explore the most common causes of this issue and their corresponding solutions:

1. Low Battery Voltage

When there’s an insufficient battery voltage, it can hinder the generator’s ability to start and maintain its operation. 

In this case, when the start button is held down, it bypasses the electrical system’s safety circuits and allows the generator to run temporarily. 

A Low battery voltage can be caused by a discharged or faulty battery, loose connections, or a defective charging system.

To address a low battery voltage:

  • Check the battery voltage using a multimeter and ensure it meets the manufacturer’s specifications.
  • Inspect the battery terminals and connections for tightness and cleanliness. Clean or tighten any loose or corroded connections.
  • Consider replacing the battery if faulty and ensure the charging system is functioning correctly.

2. Engine Oil Level

An insufficient engine oil level can also trigger safety mechanisms within the generator, causing it to shut off or not start properly. 

This safety feature is designed to protect the engine from running without sufficient lubrication.

That means if there’s no engine oil in the generator and it keeps on working, sorry to say, the generator would be beyond repair. 

To address engine oil level issues:

  • Check the oil level using the dipstick provided by the manufacturer.
  • If the oil level is below the recommended range, add more oil if it’s below the range.
  • Ensure the oil used is the correct type and viscosity recommended by the generator manufacturer.

Also Read:- Cummins Generator Engine Oil Type And Recommendations 

3. Lack of Fuel/Diesel

When the fuel/diesel level in the generator’s tank is critically low, the engine may struggle to start or maintain operation. 

This can lead to a situation where the generator only runs while the start button is held down. 

And in most cases, lack of fuel or diesel in Onan generators can cause a lot of issues like affecting the fuel injector or the carburetor as the case may be. 

To address a lack of fuel/diesel:

  • Check the fuel level in the generator’s tank and ensure it is above the minimum operating level.
  • If the fuel level is low, refill the tank with the appropriate fuel/diesel.
  • Verify that the fuel supply lines are not clogged or obstructed, preventing proper fuel flow to the engine.

4. Faulty Control Board or Relays

The control board and relays play an important role in managing the generator’s operation. If any of these parts become defective or malfunction, they can disrupt the normal start-up sequence, leading to the start button dependency issue.

To troubleshoot the control board and relays:

  • Examine the control board and relays for any visible signs of damage, such as burnt or melted components.
  • Check for loose connections and tighten them if necessary.
  • Consult a professional technician for further diagnostics and potential replacement if you suspect a faulty control board or relays.

5. Lack of Water in the Radiator

If the radiator’s water level is low or empty, the engine may overheat quickly, triggering safety mechanisms that prevent the generator from running normally. 

This can also result in the generator only running while the start button is held down, as it bypasses certain safety protocols temporarily.

To address the lack of water in the radiator:

  • Check the coolant or water level in the radiator. 
  • If the water level is low or empty, carefully add coolant or distilled water to the radiator. 
  • Inspect the radiator and cooling system for any leaks. Leaks can cause a loss of water or coolant, resulting in low levels. If leaks are detected, they should be repaired promptly.

6. Stuck or Defective Start Button

A stuck or defective start button can create a situation where the generator only runs while the button is held down. 

If the button fails to return to its default position after being pressed, the electrical contacts may remain engaged, preventing the generator from operating normally.

To address a stuck or defective start button:

  • Inspect the start button for any physical damage or sticking.
  • Gently press and release the button several times to ensure it returns to its default position smoothly.
  • If the button appears defective, it may require replacement. 

7. Wiring Issues

Faulty wiring connections, such as loose or corroded terminals, damaged cables, or frayed wires, can interrupt the electrical flow necessary for the generator to start and continue running. 

These issues can create intermittent connections, causing the generator to stop running once the start button is released.

To address wiring issues:

  • Thoroughly inspect the generator’s wiring connections, paying close attention to the terminals, cables, and connection points.
  • Look for any signs of damage or corrosion and replace or repair as needed.
  • Ensure all connections are secure and tight, and there are no exposed or frayed wires.

Professional Assistance and Warranty Considerations

If you have exhausted the troubleshooting steps mentioned above and are still unable to resolve the issue, it is advisable to seek professional assistance. 

Certified technicians with expertise in generator repair can diagnose complex problems, perform advanced testing, and offer appropriate solutions. 

Additionally, if your Onan generator is still under warranty, you must consult the manufacturer or an authorized service center to avoid voiding the warranty coverage.

Final Thought 

Experiencing an Onan generator that only runs while holding the start button can be frustrating, but with a systematic approach to troubleshooting, you can identify and resolve the underlying causes. 

By checking the battery voltage, inspecting the control board and relays, assessing the start button mechanism, checking the fuel, oil, and radiator, and also investigating wiring connections, you increase the likelihood of finding and fixing the problem. 

Remember, if the issue persists or if you are uncertain about any aspect of the troubleshooting process, it is always recommended to seek professional assistance. 

With proper maintenance and timely repairs, your Onan generator will continue to provide reliable power when you need it most.

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