Summary
P0440 is a general EVAP system fault code — the PCM detected a problem with the vapor recovery system but can't narrow it to a specific leak size or component. The most common causes are a loose gas cap (35%), a failed purge or vent valve (30%), and EVAP hose damage (20%). P0440 often appears alongside more specific codes (P0441, P0442, P0455) — diagnose those first if present. Start by checking the gas cap and clearing the code.
Severity: Low — emissions only
Safe to drive: Yes — no drivability impact
Repair cost: $5–$300 depending on cause
DIY difficulty: Easy to Moderate
What does P0440 mean?
P0440 is the catch-all EVAP fault code. Where P0442 and P0455 specify a leak size, and P0441 specifies a purge flow problem, P0440 simply says "something is wrong with the EVAP system." Some manufacturers use P0440 as their only EVAP code; others set it alongside more specific codes.
The EVAP system captures fuel vapors from the gas tank in a charcoal canister and routes them into the engine to be burned. The PCM periodically tests the system's integrity. P0440 means that test failed, but the specifics depend on what other codes are present.
If P0440 is the only code, treat it as a general EVAP leak/malfunction and work through the causes systematically.