Generac GP15500EFI / GP18000EFI error codes
6 codes from the official Generac manual (Owner's Manual for Portable Generator), each with the manual page. For 5 of them the manual says to contact an authorized service dealer.
Applies to: Generac GP15500EFI, Generac GP18000EFI.
| Code | What it means | What to do | Service | Manual |
|---|---|---|---|---|
| 1-1 CO Monitor | Carbon monoxide is above the limit, or input voltage to the COsense module is below normal range. COsense shuts off the engine when CO accumulates. | Move generator outside, away from windows, doors, and vents, and point the exhaust away from people and buildings. Contact an IASD. | dealer | p. 9 |
| 1-2 Battery Voltage | Battery voltage is above the normal operating range. | Contact an IASD. | dealer | p. 9 |
| 1-3 Battery Voltage | Battery voltage is below the normal operating range. | Charge the battery to the correct level. | owner | p. 9 |
| 5-2 Engine Speed | No or low fuel, or engine speed is below the normal operating range. | Fill the fuel tank. If the fault persists, contact an IASD. | dealer | p. 9 |
| 6-1 Engine Oil Pressure | Low oil pressure, or the oil pressure switch voltage is not detected. The low oil pressure shutdown system stops the engine. | Fill the crankcase to the correct oil level. Contact an IASD. | dealer | p. 9 |
| Other Multiple | Multiple faults are present. The manual lists no specific condition for this entry. | Contact an IASD for the full list of fault codes. | dealer | p. 9 |
IASD: Independent Authorized Service Dealer, the brand-certified service company.
Source: official Generac manual, read 2026-11-02. "Owner" means the manual lists steps you can take; "dealer" means it directs you to authorized service. Fuel, gas and electrical work on generators is for qualified technicians; follow the manual's safety section.