Emission controls · Powertrain · generic (SAE-defined)
P0440: Evaporative Emission System
P0440 means the engine computer has detected a general fault in the evaporative emission (EVAP) system, which captures fuel vapor from the tank and burns it in the engine.
Standard title per SAE J2012 / ISO 15031-6 · Updated 2026-11-07 · By CarWhere Research
How P0440 sets
The powertrain control module (PCM) runs EVAP self-tests, typically after a cold soak, by sealing the system with the vent valve and using engine vacuum or a pump to check whether it holds pressure or vacuum. It also checks that the purge and vent components respond. If a fault is found that does not fit a more specific code, the PCM sets P0440. Test conditions vary by manufacturer.
Common causes of P0440
Roughly most likely first; the actual cause depends on the vehicle and needs testing to confirm.
- Loose, damaged, or incorrect fuel cap
- Leaking EVAP hoses or connections
- Faulty purge valve or vent valve
- Cracked or saturated charcoal canister
- Faulty fuel tank pressure sensor
- Damaged filler neck
P0440 symptoms
- Check engine light on
- Possible fuel odor near the vehicle
- Usually no drivability symptoms
How P0440 is diagnosed
- Check the fuel cap for proper seating, a damaged seal, and correct type
- Scan for other EVAP codes that point to a specific component
- Visually inspect EVAP hoses, canister, and filler neck for cracks or disconnections
- Command the purge and vent valves with a scan tool and verify operation
- Perform a smoke test of the EVAP system to locate leaks
- Check fuel tank pressure sensor readings for plausibility
Typical fixes for P0440
- Tighten or replace the fuel cap
- Replace leaking hoses or seals
- Replace the purge or vent valve
- Replace the charcoal canister or filler neck
Replace parts only after testing confirms the cause — a code names the circuit or condition that failed a check, not necessarily the faulty part. We don’t publish per-repair prices; for what households actually spend on upkeep, see car repair costs.
Manufacturer notes
Definitions can vary by manufacturer; check factory service information. Newer SAE wording for this code is "Evaporative Emission System."
Related codes & warning lights
P0440 FAQ
What does code P0440 mean?
P0440 means the engine computer has detected a general fault in the evaporative emission (EVAP) system, which captures fuel vapor from the tank and burns it in the engine. The standard definition is "Evaporative Emission System."
Can I drive with a P0440 code?
Yes. This is an emissions code that rarely affects how the vehicle drives. You may notice a fuel smell, and the vehicle will likely fail an emissions inspection until it is fixed.
What does the EVAP system do?
It stores gasoline vapor from the fuel tank in a charcoal canister and later draws those vapors into the engine to be burned, instead of venting them to the atmosphere.
Will P0440 clear on its own after I fix the cap?
Often yes after several drive cycles in which the EVAP test runs and passes, though the test may require specific conditions such as an overnight cold soak.
Keep researching
More emission controls codes
Sources
- SAE J2012 — Diagnostic Trouble Code Definitions (standard code titles)
- ISO 15031-6 — Road vehicles: communication between vehicle and external equipment for emissions-related diagnostics, Part 6: Diagnostic trouble code definitions
- U.S. EPA — Vehicle Emissions Inspection and Maintenance (I/M) programs
- U.S. EPA, 40 CFR 86.1806-17 — Federal onboard diagnostics requirements for light-duty vehicles
- California Air Resources Board — On-Board Diagnostic (OBD) Program
General information written by CarWhere Research, not a diagnosis of your vehicle. Manufacturers can add their own sub-definitions and test conditions; confirm with the factory service information for your year, make and model. Before paying for a repair, check NHTSA for open recalls and your warranty booklet: federal law requires an emissions warranty on major emission-control parts such as the catalytic converter and engine computer.