How To Fix Generac Home Backup & Generator RPM Sense Loss Error?

Generac home backup generators are designed to automatically provide power to your home during utility power outages. However, these generators can sometimes display error codes that require troubleshooting and repairs. One common Generac diagnostic code is the RPM sense loss alarm.How To Fix Generac Home Backup & Generator RPM Sense Loss Error?If your Generac generator displays blinking red lights and the code “RPM Sense Loss”, this indicates the generator’s engine RPM sensor is not working properly. The RPM sensor monitors the generator’s shaft speed to ensure the engine is running at the correct revolutions per minute. When the RPM signal is lost or interrupted, the generator control panel will show the RPM sense loss error and prevent the generator from starting or continuing to run.

Resetting the alarm and fixing the underlying RPM sensor issue is important to ensure your backup generator operates properly when you need it most. This article will cover the common causes of Generac RPM sense loss, steps to reset the alarm code, tips to troubleshoot and test the RPM sensor, and preventative maintenance to avoid future issues. Follow along to learn how to quickly resolve Generac RPM sense loss errors and keep your home generator running smoothly.

What Causes the RPM Sense Loss Error?

There are several possible causes for the RPM sense loss error on Generac home standby generators:

  • Faulty RPM sensor: The RPM sensor that monitors the generator’s engine speed may be defective and need replacement. This is the most common cause of persistent RPM sense loss errors.
  • Disconnected RPM sensor wiring: The wiring that connects the RPM sensor to the generator control board may be loose, disconnected, or damaged, interrupting the signal.
  • Control board issues: Problems with the generator control board can prevent reading the RPM signal properly, throwing a false alarm.
  • Damaged generator shaft: If the generator’s engine shaft is bent or damaged, it can disrupt the RPM sensor reading.
  • Generator overspeed: The RPM sensor threshold may have been exceeded due to a runaway overspeed condition, requiring a reset.
  • Loose generator parts: Internal loose parts like belts, pulleys, and hardware can sometimes cause RPM signal interruptions.
  • Poor electrical grounding: Insufficient generator grounding can affect electronic sensor signals like the RPM reading.

Any of these issues can trigger the RPM Sense Loss error code to display on your Generac home generator.

How to Reset Generac RPM Sense Loss Alarm

Before troubleshooting the root cause, the first step is resetting the red blinking RPM Sense Loss alarm on your Generac generator. Here is a step-by-step guide to resetting the alarm:

Step 1: Turn Off the Generator

  • Locate the main generator circuit breaker and switch it to the “Off” position.
  • Make sure the generator engine has fully shut down before proceeding.

Step 2: Disconnect All Loads

  • Turn off and disconnect all electrical loads connected to the generator including home circuits, HVAC systems, sump pumps, etc.
  • Disconnecting all loads helps prevent accidental shock or damage.

Step 3: Inspect the Generator

  • Open the generator housing and thoroughly inspect for any loose wiring connections, damaged cables, or broken parts.
  • Make repairs if any obvious issues are found.

Step 4: Press the Enter Button

  • The enter button is located on the generator control panel, often near the display.
  • Press and hold the Enter button for 5-10 seconds until the alarm light turns off.
  • This should reset the control board and clear the RPM Sense Loss error code.

Step 5: Restart the Generator

  • Reconnect electrical loads if needed.
  • Start up the generator and confirm normal operation without the RPM Sense Loss alarm returning.

Following this process should reset and temporarily clear the RPM alarm code so further diagnosis can be performed. If the alarm comes back immediately, it indicates a problem still exists requiring repair.

Troubleshooting RPM Sense Loss on a Generac Generator

Once the alarm is reset, the next step is running diagnostic tests to pinpoint the root cause of the RPM Sense Loss error. Here are the main troubleshooting steps:

Inspect Sensor Wiring

  • With the generator shut down, locate the RPM sensor wiring harness.
  • Check that the connections to the sensor and control board are intact with no loose, broken, or cut wires.
  • Measure continuity through the wiring to confirm no breaks exist.
  • Repair or replace damaged RPM sensor cables as necessary.

Check RPM Sensor Resistance

  • Using a multimeter, measure the resistance through the RPM sensor on the generator. Consult the generator manual for specific ohm reading range.
  • Readings outside the specified range usually indicate a bad RPM sensor that needs replacement.

Monitor Sensor Output Voltage

  • Connect a multimeter to the RPM sensor signal wire while the generator is running.
  • Verify the sensor outputs 0-5V fluctuating voltage on the signal wire proportional to engine speed.
  • If voltage is zero or flatlined, it signifies a defective sensor.

Test Sensor with Oscilloscope

  • For full diagnosis, connect an oscilloscope to monitor the RPM sensor output while running.
  • Look for clean sine wave signals with amplitude proportional to engine RPM.
  • Irregular waveforms indicate issues with the sensor or wiring at fault.

Check for Engine Damage

  • With the generator off, remove the starter housing and physically inspect the engine shaft and couplings.
  • Check for any bent components, broken couplings, or damaged bearings that could affect the RPM sensor reading.
  • Replace any damaged engine components and retest generator operation.

Following these troubleshooting steps will help narrow down whether the issue is with the RPM sensor itself, wiring connections, or generator engine.

How to Replace a Faulty RPM Sensor

If testing confirms the RPM sensor is defective, replacement of the sensor is needed:

Buy the Correct Replacement Sensor

  • Consult your generator manual or the RPM sensor part number to purchase the right sensor for your Generac model.
  • Avoid using aftermarket sensors that may not provide accurate and reliable readings.

Shut Down and Disconnect the Generator

  • Turn off the generator at the breaker and disconnect all loads. Allow engine to fully cool before service.

Locate and Remove the Old Sensor

  • Find the RPM sensor mounted near the generator engine shaft or flywheel housing.
  • Disconnect the sensor wiring harness and unscrew the sensor mounting hardware.
  • Remove the defective RPM sensor from the generator.

Install the New RPM Sensor

  • Screw in the new sensor using the provided hardware and tighten securely as specified by the generator manual.
  • Take care not to overtighten.
  • Reconnect the wiring harness to the sensor terminals.

Test Operation

  • Reinstall all covers and restart the generator. Let it run and verify the RPM Sense Loss error does not return on the control panel.
  • Conduct regular maintenance runs to ensure proper RPM sensor operation over time.

With the RPM sensor replaced, your Generac generator should run smoothly without recurring sensor issues. Be sure to always verify compatibility and follow generator instructions when installing a new part.

Preventing Future RPM Sensor Issues

Besides properly troubleshooting and replacing a failed RPM sensor, there are also some generator maintenance tips that can help minimize future RPM Sense Loss occurrences:

  • Perform routine generator exercise: Run the generator regularly under load to ensure internal engine parts stay lubricated and loosened up.
  • Inspect wiring connections: Check for any loose sensor wiring or damaged cables during maintenance runs that could cause intermittent electrical shorts.
  • Change oil regularly: Old dirty oil can clog small passages around the RPM sensor affecting operation. Follow the specified oil change intervals.
  • Clean or replace air filters: Clogged air filters put extra strain on the generator engine which can impact RPM sensor readings.
  • Check engine grounding: Verify the generator frame and engine components are properly grounded to avoid electrical noise in sensor signals.
  • Update firmware: Keep the generator control board firmware up to date for optimal performance with sensors and diagnostics.
  • Consult a certified technician: Have a generator expert inspect your unit annually and correct any issues found to prevent bigger problems down the road.

Following basic preventative generator maintenance and safety checks will go a long way towards avoiding cryptic RPM sense loss errors when you need your backup power the most. Refer to your complete Generac owner’s manual for further troubleshooting tips and generator care guidelines specific to your model.

Key Takeaways: Resolving Generac RPM Sense Loss

  • The RPM Sense Loss error indicates a problem with the generator engine speed sensor signal getting interrupted.
  • Resetting the alarm code requires shutting down the unit, disconnecting loads, and holding the Enter button.
  • Faulty RPM sensors, damaged wiring, loose parts, control board issues, and engine damage are common causes.
  • Thoroughly test sensor wiring, resistance, output voltage, and waveform shape to pinpoint issues.
  • Replace defective RPM sensors with an exact OEM replacement part for your generator model.
  • Preventative maintenance like exercising the generator, changing oil, cleaning air filters, and checking grounding can help avoid future sensor failure.


RPM Sense Loss is a common diagnostic code on Generac home standby generators indicating an issue with the engine speed monitoring sensor. Following the step-by-step troubleshooting and repair tips outlined in this article will help you quickly resolve RPM alarm errors. Reset the code, test sensor operation, replace damaged components if needed, and perform preventative generator maintenance to keep your unit running strong when utility power is lost. With the proper troubleshooting approach, Generac homeowners can feel confident their generator will be ready to deliver backup power whenever emergencies or outages occur.

Frequently Asked Questions

1. Why does my Generac generator keep showing RPM sense loss?
Frequent RPM sense loss errors usually indicate a problem with the RPM sensor itself or the wiring harness connections. Inspect the sensor wiring for breaks and measure sensor resistance to check for a faulty sensor needing replacement.

2. Can a Generac generator run with bad RPM sensor?
No, the generator will not start or run when it detects an RPM sensor problem or signal loss. This safety feature prevents operation without proper speed monitoring which could damage the engine.

3. How do I bypass the RPM sensor on my Generac generator?
It is not recommended to bypass or ignore the RPM sensor signal loss as this can lead to catastrophic engine damage. The proper fix is to troubleshoot and replace the faulty sensor or wiring issue causing the error.

4. What does it mean if my Generac generator has no RPM signal?
Lack of any RPM sensor signal means there is a complete wiring disconnection or the sensor has completely failed. Check all wiring connections and junctions points and test the sensor resistance and voltage output to confirm the sensor is bad.

5. Where is the RPM sensor located on a Generac generator?
The RPM sensor is typically mounted near the generator engine flywheel housing to read timing pulses off the crankshaft or camshaft. Consult your generator manual for the exact location.

6. Can a faulty RPM sensor cause my Generac generator not to start?
Yes, the generator control board will not allow starting the unit when it detects an invalid RPM sensor signal or wiring fault. Fixing the sensor issue is necessary for normal starting operation.

7. Why does my Generac generator run but shows RPM sense loss?
This usually indicates an intermittent issue with the RPM sensor wiring that only manifests occasionally. Check all wiring connections for corrosion or looseness that could explain the inconsistent signal.

8. How do I test my Generac RPM sensor?
Use a multimeter to check sensor resistance, monitor AC voltage output to confirm it fluctuates proportionally with engine speed, and connect an oscilloscope to visualize the waveform shape and amplitude changes relative to RPM.

9. Does the RPM sensor affect charging on my Generac generator?
No, the charging system uses a separate voltage regulator and stator to manage battery charging. The RPM sensor only monitors engine speed and does not directly impact charging.

10. Can bad diesel fuel cause RPM sense loss on my Generac generator?
Possibly, contaminated or stale diesel fuel can affect engine performance and cause erratic RPM readings. Drain old fuel and replace with fresh diesel from sealed containers to rule out bad fuel.

11. Why do I still get RPM sense loss after replacing the sensor?
Other possible causes could be a loose sensor mounting, defective wiring connections, control board issues, or continued engine damage affecting the sensor signal. Thorough diagnosis beyond just the sensor is needed in some cases.

12. Is it safe to disconnect the RPM sensor on my Generac generator?
No, disabling or disconnecting the RPM monitoring is strongly discouraged as it can lead to dangerous runaway overspeed and engine damage. Always repair the sensor circuit properly.

13. Where can I buy a replacement RPM sensor for my Generac generator?
Purchase a factory OEM RPM sensor through Generac or an authorized dealer for your specific generator model. Avoid cheap aftermarket sensors that may give inaccurate readings.

14. How do I program a new RPM sensor on my Generac generator?
For digital RPM sensors, no programming is needed – simply wire up the new sensor properly. For generators with a programmable control board, you may need to input the sensor part number through the user interface.

15. What is the average cost to replace a bad RPM sensor?
The parts cost is typically $50-$150 for the sensor. Add hourly shop labor rates to install for the total replacement cost. DIY repairs can save on labor costs.

16. Can RPM sensor problems cause the generator engine to stall out?
Yes, invalid RPM signals can confuse the generator controller and cause it to improperly stall or shut down the engine as a fail-safe measure. Fixing the sensor issue will restore normal operation.

17. My RPM sensor is new but the reading is still erratic – why?
Check for loose sensor wiring connections, a faulty control board, or continued engine damage like a bent shaft. Also ensure the sensor is fully compatible with your generator model.

18. I get no RPM signal at idle but it works when running – what’s wrong?
This points to a worn-out sensor that can’t accurately read lower RPMs. The sensor may be near the end of its lifespan and need replacement despite partially working.

19. What maintenance helps avoid Generac RPM sensor problems?
Frequent generator exercise, regular oil and filter changes, replacing air filters, proper grounding, updating control board firmware, and annual professional inspection/tuning.

20. Does over speeding a Generac generator cause the RPM sensor to fail?
Yes, excessive overspeed events generate very high voltages in the RPM sensor that can permanently damage its internal components leading to sensor failure.

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