Generac · Generator Critical

1501 — RPM Sense Loss

Alarm 1501 is "RPM Sense Loss" — the controller could not read a valid engine RPM signal during cranking or running, so it shuts down. It is not specifically an under-frequency (<58 Hz) trip; under-speed/under-frequency is a separate alarm.

Keep using it?
No — service first
DIY difficulty
Hard
Verified against
generac.com ↗

How to fix it

  1. Check and load-test the starting battery (a weak battery is a common cause).
  2. Inspect the speed/RPM (magnetic pickup) sensor and wiring.
  3. Verify fuel delivery; have a Generac dealer diagnose if it persists.

Why it happens

Typical signs: 1501 / RPM Sense Loss in the alarm log · Generator cranks but shuts down, or will not stay running · Unit fails to complete a start

  • No valid RPM signal reaching the controller Failed/dirty speed (magnetic pickup) sensor, wiring, or a battery too weak to crank to firing speed.
  • Engine not reaching/holding firing speed Fuel delivery, valve, or mechanical issue preventing a clean start.

Parts you may need

If diagnosis points to a failed part, these are the common replacements. As an Amazon Associate we earn from qualifying purchases.

  • Air filter (10 kW air-cooled) Common replacement
    Amazon →

More Generac generator codes

1100 1100 — Overcrank (Engine Failed to Start) 1300 1300 — Low Oil Pressure Shutdown 1505 1505 — Overcrank (Variant — Try Again) 1600 1600 — Underspeed 1800 1800 — Overvoltage 1900 1900 — Undervoltage

All Generac codes → All generator codes →

Always unplug an appliance before servicing it. This guide is for informational purposes and is not a substitute for a qualified technician. Verified against manufacturer documentation: generac.com.