1505 Serious Moderate DIY

Generac Generator 1505 — Overcrank (Variant — Try Again)

Generac Generator · Error code 1505

What 1505 Means

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.

Symptoms

  • 1505 displayed
  • Unit attempted to start during weekly exercise or outage
  • Cranks but does not catch and run

Common Causes

1
Battery failing under load

Most common cause. Often shows normal resting voltage but collapses during crank — load test, don't just read voltage.

2
Corroded or loose battery / starter contactor connections

Voltage drop at the terminals or contactor prevents a clean crank and RPM signal.

3
Starter motor fault

Slow, weak, or non-engaging starter means the controller never senses cranking RPM.

4
Damaged RPM-signal wiring (wire 18)

Rodent damage, corrosion, or a loose connector interrupts the engine-speed signal to the controller.

How to Fix It

  1. 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.
  2. Clean and tighten the battery terminals and check the starter contactor connections for corrosion or looseness.
  3. Inspect the RPM-signal wiring (wire 18) and its connectors for rodent damage, chafing, or corrosion.
  4. 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.
  5. If the engine cranks normally and 1505 returns, have a dealer diagnose the RPM-sensing circuit (ignition coils/flywheel signal or controller).

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.

Common replacement Replacement battery View on Amazon→ Common replacement Spark plug NGK BPR5ES View on Amazon→

More Generac Generator Codes

0000 0000 — No Active Alarm (Healthy) 1100 1100 — Low Oil Pressure Shutdown 1300 1300 — High Engine Temperature 1500 1500 — Overcrank 1501 1501 — Underspeed 1600 1600 — Overspeed

All Generac codes → All generator codes →

Verified against manufacturer documentation: generac.com

Always unplug an appliance before servicing it. This guide is for informational purposes and is not a substitute for a qualified technician.