Generac generator code 1501 / 1505 / 1511 / 1515

High severity — The controller lost the RPM/timing signal it uses to confirm the engine is actually turning — either the engine stalled while running or never produced a usable signal while cranking.

Applies to: Guardian/Protector series generators with 1- or 2-cylinder engines on an Evolution controller (the exact 4-digit code depends on cylinder count and whether it happened while running or cranking)

What it means

Four different code numbers, one underlying alarm. Which digits show up on your display depends on two things the controller already knows about your unit: how many cylinders the engine has, and whether the loss of signal happened during cranking or after the engine was already running. 1505 and 1515 are the cranking versions for 2-cylinder and 1-cylinder units respectively; 1501 and 1511 are what shows up if the engine had actually started and then lost the signal.

The controller lost the RPM/timing signal it uses to confirm the engine is actually turning — either the engine stalled while running or never produced a usable signal while cranking.

That distinction matters for diagnosis. If it's the cranking version, treat it like any other failed-start fault first. If it's the running version, something interrupted an engine that was genuinely operating — which points more toward a sensor or wiring problem than a fuel problem.

Most common causes

A shortlist, since the fix usually isn't complicated once you know which end of it you're dealing with:

Engine actually stalled (fuel starvation, fouled plug, ignition failure)
Faulty or misaligned crankshaft/flywheel speed sensor
Damaged wiring or a corroded connector at the sensor
Debris on the flywheel's sensor ring

What you can check yourself

Start with the same basics as any no-start, then narrow it down:

Check for the same fuel and ignition issues you'd check for an overcrank fault (fuel supply, spark plug condition)
Inspect the sensor's wiring harness for chafing or a loose connector near the flywheel housing
Clear the fault at the controller and attempt a restart

Fuel and spark hazards apply here too.

If you smell raw fuel while checking a cranking-version fault, stop and don't attempt another start.
Disconnect the battery before working anywhere near the flywheel housing or sensor wiring — an unexpected crank near exposed skin or clothing is a real injury risk.

Call a professional when: If the engine sounds like it's actually running fine but the fault still triggers, the RPM sensor itself (or its air gap to the flywheel) is the likely culprit and is best adjusted or replaced by a technician with the correct gap-setting tool.

All codes for this brand

Every Generac generator fault code — full list with what differs between models.

Related codes and symptoms

Generac code 1100 — Overcrank, the closest relative among the failed-start codes
Generac Low Battery warning, since weak battery voltage is one of the more common root causes here
Generac Charger Warning, worth a look if battery voltage keeps drifting low between outages
Symptom: Generator Won't Start — general troubleshooting if you're not certain which 4-digit code is on your display

Sources

Generac Support: "RPM Sense Loss, error codes 1500-1521"

This site is an independent reference and is not affiliated with, endorsed by, or sponsored by any generator manufacturer. It is not a substitute for a licensed electrician or generator technician. Standby and portable generators involve mains-voltage output and, on LP/NG units, a live fuel-gas supply — work on wiring, the transfer switch, or the fuel system should be done or verified by someone qualified to do it. Pages are written with AI assistance from the sources listed on each page and checked against them before publishing.