Generac Generator 1903 Error Code Explained: Meaning, Causes & Fixes

 

Understanding the 1903 Error Code on a Generac Generator

 

When your Generac generator displays the 1903 error code, it is indicating an “Under-speed” or “RPM Sense Loss” fault. In simple terms, this means that the generator's engine is not running at the correct speed, or the control system is unable to detect how fast the motor is spinning. Generators need to run at a specific speed to produce the right amount of electricity (measured in hertz); when they slow down, speed up unexpectedly, or lose the ability to detect their own speed, it can result in problems with power output or even damage sensitive appliances.

 

What Causes the 1903 Error Code?

 

A 1903 fault usually occurs because:

• There is a problem with the speed sensor, also called the RPM sensor, which tells the generator's computer how fast the engine is working.
• The engine itself is failing to maintain a consistent speed—often due to fuel supply issues, mechanical problems, or improper load.
• Corrosion, loose wiring, or broken connectors are preventing electrical signals from reaching the control board.
• There is a problem with the electronic control board inside the generator.

This error code can be seen in both home and business backup Generac units, and is a frequent service call in both St Louis and Nashville, especially during peak seasons for storms or power outages.

 

Signs and Symptoms Linked to 1903 Fault

 

When the 1903 code appears on your Generac generator, you might notice:

• The generator tries to start but shuts down quickly.
• An alarm or warning light may flash on the control panel.
• You may not have any backup power when the main power goes out.
• The display panel will usually read "Under-speed," "RPM Sense Loss," or specifically show “1903” as the error code.

Customers in St Louis and Nashville often report that the generator seems to “struggle” or make unusual sounds just before this error appears.

 

Common Causes Specific to Generac Generators

 

• Dirty or Clogged Air Filter – Airflow restriction makes it hard for the engine to breathe, leading to low speed.
• Fuel Pressure Problems – Low or inconsistent fuel flow (natural gas or propane) may starve the engine, making it run slow or stall.
• Mechanical Engine Problems – This could include issues with the throttle, governor, spark plugs, or ignition coil failing to keep the speed constant.
• Faulty or Disconnected RPM Sensor – The sensor that tells the generator how fast it’s spinning might be broken, dirty, or have a bad connection.
• Electrical Connection Issues – Vibration, corrosion (especially in humid areas like Nashville), or rodent damage to wires can interrupt signals.
• Control Board Failure – Less common but possible, the main electronic “brain” of the unit could be malfunctioning.

 

What Should I Do if My Generator Shows 1903?

 

If you see the 1903 fault code, here are steps you can take before calling a technician:

• Turn the generator off completely—flip the switch to the “OFF” position and wait a few minutes.
• Visually inspect the unit for obvious damage, loose wires, or debris around air intake and exhaust areas.
• Check or replace the air filter if you are comfortable doing so.
• If accessible, check for leaks in fuel lines or a closed fuel valve (make sure the fuel is turned on).
• After checking, switch the generator back to “AUTO” mode and try a manual start.

If the generator still displays the 1903 error code or does not start properly, do not attempt advanced repairs yourself. If you are in St Louis or Nashville, contact a professional generator service like Hoffman Brothers for reliable and safe troubleshooting and repair.

 

Why Professional Inspection is Important

 

Gasoline, propane, or natural gas generators can pose safety hazards such as electric shock, fire, or gas leaks. The 1903 error involves many components—fuel system, wires, electronic boards, and moving parts. An experienced technician will:

• Use diagnostic tools to confirm if the engine is actually running slow or if it’s a false signal from wiring or the RPM sensor.
• Check electrical and sensor connections for corrosion, looseness, or rodent damage.
• Test the air-fuel mixture, engine operation, and load balance.
• Inspect and clean or replace RPM sensors and related components as needed.
• If necessary, reprogram or replace the generator’s main control board.

Homeowners in both St Louis and Nashville find that professional generator maintenance can prevent most error codes and ensure the unit is always ready for outages.

 

Preventing Future 1903 Errors

 

Regular generator maintenance—changing filters, checking fuel supply, cleaning electrical connections, and running periodic self-tests—greatly reduces the chance of experiencing a 1903 error code. Local weather in St Louis and humidity in Nashville may demand even more frequent checks for corrosion or debris. Scheduling annual professional inspections and promptly addressing any engine trouble is the best way to keep your generator reliable.

 

In Summary

 

The 1903 error code on a Generac generator means the engine is not running at the right speed or the system can’t detect its speed. This often involves minor sensor or wiring issues, but can be caused by deeper engine or fuel problems. While there are a few quick things you can check yourself, it’s safest to call in a certified generator specialist, especially for residents and businesses in regions like St Louis and Nashville. Regular service and prompt attention to warning codes will protect your backup power source for years to come.