1505 — Overcrank (Variant — Try Again)
The controller lost the engine RPM signal during a crank cycle (RPM Sense Loss). The unit shuts down and the alarm will not self-clear — it must be cleared manually at the controller before the generator will attempt to start again. The most common cause is a battery that reads normal voltage at rest but collapses under cranking load.
- Keep using it?
- Limited use only
- DIY difficulty
- Moderate
- Typical cost
- $45-70
- Verified against
- generac.com ↗
The fix
Generac 12V AGM starting battery (0G9449 or model-specific equivalent)
Lost engine RPM signal during crank — usually a weak battery collapsing under cranking load
Diagnose first: Confirm your exact battery part number/size for your model before ordering — Generac uses different battery capacities across unit sizes. A battery that reads normal resting voltage but sags under cranking load is the single most common cause of this alarm. This alarm must be manually cleared at the controller after the fix.
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How to fix it
- Load-test the battery — a failing battery can read 12.5V+ at rest and still collapse during crank. Confirm it holds >9.6V while cranking; charge or replace as needed.
- Clean and tighten the battery terminals and check the starter contactor connections for corrosion or looseness.
- Inspect the RPM-signal wiring (wire 18) and its connectors for rodent damage, chafing, or corrosion.
- Clear the alarm at the controller (per the manual, e.g. ENTER/OFF on Evolution controllers) — 1505 latches and the unit will not retry until cleared — then retest with a manual start.
- If the engine cranks normally and 1505 returns, have a dealer diagnose the RPM-sensing circuit (ignition coils/flywheel signal or controller).
Why it happens
Typical signs: 1505 displayed · Unit attempted to start during weekly exercise or outage · Cranks but does not catch and run
- Battery failing under load Most common cause. Often shows normal resting voltage but collapses during crank — load test, don't just read voltage.
- Corroded or loose battery / starter contactor connections Voltage drop at the terminals or contactor prevents a clean crank and RPM signal.
- Starter motor fault Slow, weak, or non-engaging starter means the controller never senses cranking RPM.
- Damaged RPM-signal wiring (wire 18) Rodent damage, corrosion, or a loose connector interrupts the engine-speed signal to the controller.
Other parts sometimes needed
If diagnosis points to a failed part, these are the common replacements. As an Amazon Associate we earn from qualifying purchases.
More Generac 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.