Generac error code 1505 RPM sense loss explained & how to fix

Generac, Guardian, Honeywell, Siemens, Centurion, Watchdog, Bryant, & Carrier Air Cooled Home Standby generator troubleshooting and repair questions
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Because the 1505 error code alarm on Generac is such a popular question I wanted to explain what this means and why it happens...

The error code 1505 is a RPM loss alarm and will trigger a shutdown anytime it occurs and will not self clear. It's a CRANKING alarm, which means that the alarm occurred during a crank cycle, NOT while the unit was actually running. This is usually caused by a couple of simple things.

1. The battery is bad, dead, not connected properly, or has loose or dirty terminals.
2. The starter contactor has a problem or loose connection. This is located near the controller and is a small black colored relay with 4 wires. It converts the controller's start signal into a higher current signal that turns the starter's solenoid on.
3. The starter motor has a problem, bad connection or the small 16 wire which tells the solenoid to turn on is loose or disconnected.
4. The ignition coils have a problem. This could be that they are bad, have contacted the flywheel, etc. The 18 wire sends the RPM signal to the Evolution from the ignition coils.
5. The engine (however unlikely) is internally damaged and will not physically move (seized up)

During troubleshooting, always start with the battery. It's the most likely cause and should be load tested, not just checked for voltage. A bad battery will very often show normal battery voltage but when a load is applied will drop to zero, or well below the normal threshold for a battery. If the battery checks out, see other causes above and move on from there checking cables and connections.

If you have more questions, please start a new thread with your generator's information (serial number/model) so that we can better help you!
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