P0440

P0440 is the OBD-II diagnostic trouble code for Evaporative Emission Control System Malfunction. It indicates that the engine control module detected a fault within the EVAP system, which is responsible for capturing fuel vapors from the fuel system and routing them for combustion rather than releasing them to the atmosphere. The fault is broad and may arise from a minor issue or a more significant leak or component failure. When triggered, the vehicle’s check engine light typically comes on and the vehicle may fail an emissions test.

The EVAP system includes components such as the fuel tank, charcoal canister, purge valve, vent valve, associated hoses and lines, and sensors. The system can be upset by leaks, a faulty purge or vent valve, a weak or failed pressure sensor, damaged hoses, or a loose or degraded gas cap. Wiring or connector problems can also trigger the code.

Common symptoms include a illuminated check engine light and, in some cases, a noticeable fuel odor or a failed emissions inspection. Many EVAP faults do not produce obvious drivability problems, though a large leak or faulty valve can cause starting or idle issues in some vehicles.

Diagnosis typically begins with a scan for codes and a visual inspection of the gas cap and EVAP hoses. A more thorough test may involve a pressure or smoke test to locate leaks, and testing or replacement of EVAP components such as the purge valve, vent valve, canister, or sensors. After repairs, codes should be cleared and a drive cycle performed to verify the fault is resolved.