Generac GP18000EFI
Generator. Specs from the manufacturer page (checked ).

The Generac GP18000EFI is a portable generator with 18,000 W running output and 22,500 W starting output, powered by an 816cc engine with Electronic Fuel Injection. The manufacturer rates it at up to 9 hours of runtime at 50% load. It has electric start with the battery included and a never-flat wheel kit for moving it around.
Key features
- 816cc engine with Electronic Fuel Injection
- Up to 9 hours of runtime at 50% load
- TruePower Technology with less than 5% THD for sensitive electronics and tools
- COsense Technology for protection against hazardous carbon monoxide
- Electric start with battery included
- Low-oil pressure shutdown protects the engine
- Circuit breaker protected outlets
- Large fuel tank of 14.2 gal (54 l) with fuel gauge
What it is for
- Emergency home backup
- DIY projects
- Jobsite use
Specifications
| Running watts | 18000 W |
|---|---|
| Peak / surge | 22500 W |
| Tank | 54 L (14.3 gal) |
| Run time at 50 % load | 9 h |
| CO shutoff | Yes |
| AC output voltage | 120/240 VAC |
| Weight | 200.9 kg (442.9 lb) |
| Dimensions | Length 39.5 in (100.3 cm), Width 30.9 in (78.5 cm), Length 36.5 in (92.8 cm) |
From the Generac page. Values the manufacturer does not publish are left out.
What is in the box
- Never-flat wheel kit
- Battery for electric start
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Connection and wiring
Follow the diagrams in the Generac manual. Connecting to a home panel needs a transfer switch or interlock and a licensed electrician.
Error codes and troubleshooting
| Code | Meaning | What to do | Manual page |
|---|---|---|---|
| 1-1 | 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. Call service if it persists. | 9 |
| 1-2 | Battery voltage is above the normal operating range. | Contact an IASD. Call service if it persists. | 9 |
| 1-3 | Battery voltage is below the normal operating range. | Charge the battery to the correct level. | 9 |
| 5-2 | No or low fuel, or engine speed is below the normal operating range. | Fill the fuel tank. If the fault persists, contact an IASD. Call service if it persists. | 9 |
| 6-1 | 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. Call service if it persists. | 9 |
| Other | Multiple faults are present. The manual lists no specific condition for this entry. | Contact an IASD for the full list of fault codes. Call service if it persists. | 9 |
From the Generac manual. All 6 GP15500EFI / GP18000EFI codes →
FAQ
How long does the Generac GP18000EFI run on a tank?
The maker rates it at 9 hours at 50 % load (about 9,000 W) on a 14.3-gal tank. A light load such as a refrigerator and lights runs longer; a full load runs shorter.
Can the Generac GP18000EFI start a sump pump or well pump?
Starting surge matters more than running watts: this unit is rated 22500 W peak. That covers a typical 1/2 HP sump pump (about 2150 W to start). Use the calculator with your exact pump.