P0440 Evaporative Emission Control System Malfunction

P0440 points to a general EVAP-system malfunction. It means the evaporative-emissions monitor failed, but the exact leak or flow problem needs further testing.

Code details

Generic OBD-II · P0

System: Emissions
Code type: Generic (SAE / ISO controlled)
Standard: SAE J2012 / ISO 15031-6

Diagnostic boundary

A diagnostic trouble code reports that a monitored test failed. It does not prove one specific part is bad, and manufacturer logic can add vehicle-specific conditions.

Do not stop at the gas cap if the code returns; P0440 can come from many EVAP plumbing, valve, wiring, or sealing faults.

Symptoms of P0440

Check-engine light, often with no obvious change in how the car drives.
A failed emissions test or incomplete readiness monitors.
Sometimes a faint fuel-vapour smell (on EVAP codes).

Common causes of P0440

A worn catalytic converter or an oxygen/air-fuel sensor reading out of range.
EVAP leaks — a loose or failed gas cap, cracked hose, or purge/vent valve.
Exhaust leaks, fuel-trim problems, or a fault in a related monitor.

Useful checks before replacing parts

Check fuel cap sealing where applicable, EVAP hose routing, purge valve behavior, vent valve operation, and tank-area connections.
Use smoke testing or the vehicle-specific EVAP test routine when a visual inspection does not find the fault.
Review related EVAP codes because they often narrow the fault to leak size, purge flow, or vent control.

Related OBD-II codes

These nearby emissions entries can help compare wording and pin down the fault area.