Generac Generator RPM Sense Loss: Causes And Troubleshooting Guide

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RPM sense loss comes in different codes depending on your generator; you can find codes 1501, 1505, 1511, or even 1515.

It is one of the issues faced by most Generac generator owners, and troubleshooting it might seem tricky as different factors can cause your generator to experience it.

The Generac generator’s RPM sense loss can be caused by different factors, including:

  • The battery
  • Starter contactor 
  • Starter motor 
  • Ignition coil
  • Or the engine itself.

Hence, in this article, we’ll identify the causes of RPM loss on your Generac generator and provide you with troubleshooting tips tailored to fix it. Let’s get started.

What’s the RPM Sense All About?

Generac Generator RPM Sense Loss,

Most users have complained about their generator bringing out rpm sense loss whenever it wants to exercise or run, and sometimes they wouldn’t see anything because they reset the generator.

In short, sometimes identified generators will randomly bring out rpm sense loss during their weekly test exercise but crank normally each time they want to run it.

Some also complained that their battery is full, and sometimes instantly, it will bring out this code “rpm sense loss,” and when they continue cranking the generator, the cranking will keep reducing till it finally stops.

While all these complaints by Generac generator owners seem to be identifying one thing: RPM sense loss, before troubleshooting it, there’s a need for us to know the actual reason why the generator brought out such a fault.

But what’s the RPM Sense loss all about?

The RPM sense loss is an alarm on Generac generators with error codes 1501, 1505, 1511, or 1515. It occurs during the crank cycle, not while the unit is running.

After understanding what rpm sense loss is all about, let’s talk about why it happens and how you can troubleshoot and fix the issue.

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Why Does Your Generac Generator Develop RPM Sense Loss And How to Fix It?

At the beginning of this blog post, we listed the various reasons that might cause your Generac generator to develop this fault. Now, let’s talk in detail about the reasons and what you should do to fix the issue.


The battery is one of the common causes of rpm sense loss on Generac generators. Either the battery is bad, dead, not fully charged, not properly connected, or has dirty or loose terminals.

And, since the battery is mostly the cause of this issue, whether it has been a long time since you used the generator or you don’t normally check the battery, it’s the first thing you should diagnose before any other things.

To fix this issue:

  • Firstly, identify if your generator battery is bad. If it is, ensure you change the battery to a good one.
  • Next, check the battery connections for any corrosion or dirt at the terminals. If there is, disconnect the wire, clean the terminals with a small wire brush, and make use of battery corrosion preventative.
  • Lastly, make sure it tightens appropriately. If it’s not tightened enough, it will cause the generator not to crank as required, developing a rpm sense loss fault.

After you have fixed the battery issue, try resetting your generator. If it still develops the error code, you can check out the remaining causes.

Also Read:- Generac Generator Not Charging Battery: Troubleshooting Guide

Starter Contactor 

 Generac Generator RPM Sense Loss,
Image source: Generac generator manual

The starter contactor is responsible for initiating the generator’s cranking process. If it encounters any issues or has a loose connection, it will prevent the generator engine from starting or cranking. You can find the starter contactor located near the controller, where the starter motor is also situated.

To diagnose whether the starter contactor is causing the generator’s RPM sense loss, inspect the starter connector cables, especially those running from the battery to the starter motor.

The starter connector consists of four (4) black-colored relay wires. Ensure these wires are securely connected to the starter connector and are free from dirt or corrosion.

If you find any cables that are dirty or corroded, make sure to remove them and clean both the cable terminals and terminal studs. If any cable is found to be defective or badly corroded, it should be promptly replaced.

Once the inspection and cleaning of the starter connector are complete, use a DC voltmeter to test it. Follow the steps below for the testing process:

Generac Generator RPM Sense Loss,
Image source: Generac generator manual
  1. Firstly, connect the voltmeter’s positive lead to the starter connector stud where the red battery connects. While keeping the positive lead connected, attach the common or negative test lead to a clean frame ground. The voltmeter should indicate a battery voltage of 12 VDC.
  1. Secondly, after testing the connector from the battery side, attach the positive (+) meter test lead to the starter contactor stud where the starter motor cable attaches. Connect the common (+) test lead to the frame ground as well. Initially, no voltage should be indicated. After completing this step, set the AUTO-OFF-MANUAL switch to MANUAL. The meter should now indicate the battery voltage as the starter contactor energizes.

Note: If battery voltage was indicated in Step 1 but NOT in Step 2b, replace the starter contactor. Additionally, if the battery voltage was indicated in Step 2b but the engine did NOT crank, it is advisable to seek the assistance of a professional.

Starter Motor

Generac Generator RPM Sense Loss: Causes And Troubleshooting Guide
Image source: Generac generator manual

Thirdly, after you have checked the starter connector and probably reset the generator, your generator is supposed to clear the error code and start, except if there are still issues.

And one of those issues that might also cause it not to start is if the starter motor has a problem that needs to be fixed. Some problems that could make the start motor faulty include:

  • A defective starter motor switch
  • A  broken, damaged, or weak magnet.
  • The starter drive got dirty; there’s a binding or seizing condition in the starter motor bearings, etc.

Depending on the fault in your starter motor, there might be a lot of ways to fix it. If you aren’t a Generac generator dealer or a generator repair professional yourself, I would advise you to seek one.

But most importantly, before attempting anything, ensure you check the connections of the starter motor to ensure they are tightly and correctly fixed.

Also Read:- Generac Starter Solenoid Troubleshooting: Complete Guide

Ignition Coil 

If the ignition coil is faulty, it can also cause your generator to develop a rpm sense loss fault. It could be that the ignition coil has stopped working, is bad, or might have contacted the flywheel since that’s where the coil is. Which might result in the 18-wire sending the rpm signal to the evolution.

To fix this issue, inspect the ignition coil and switch, making sure they are both okay. If your Generac generator uses a spark plug, ensure you test the spark using a spark plug tester. If it’s a spark, try cranking and starting the engine.

But if the issue persists, check if there’s a free flow of gas in the generator; if there is, then it’s likely that the generator engine has developed a critical fault that needs to be inspected by a Generac generator dealer or professional, whichever comes first.

Final Thought 

Fixing a Generac generator rpm sense loss fault can be frustrating, but when you inspect the battery, starter connector, starter motor, and even the ignition coil with the fuel system, the error is more likely to stop showing on your control panel.

But when you’ve fixed all that might cause this issue and yet the problem persists, you should consult a Generac generator dealer or professional, as they have the tools and knowledge to diagnose and troubleshoot the problem.

I hope you find this article helpful. If you find any errors in this article that need adjustment, please don’t hesitate to contact us.


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