P0440 — EVAP system malfunction
The evaporative emissions system isn’t operating as expected — a broad EVAP fault that often starts with the gas cap and leak checks.
What it means in plain English
P0440 is a general EVAP system malfunction. Unlike a specific “large leak” (P0455) or “small leak” (P0456) code, P0440 means the monitor didn’t complete or the system failed a broad check. Causes overlap with other EVAP codes: cap, purge/vent valves, hoses, and canister.
Common causes
- Loose, damaged, or incorrect gas cap
- Purge or vent valve faults
- EVAP hose cracks or disconnected lines
- Charcoal canister problems
- Incomplete EVAP monitor from driving pattern (sometimes)
What you can safely check
- Click the gas cap until it ratchets; inspect the seal.
- Note whether you recently overfilled the tank (can flood the canister).
- Don’t clear codes repeatedly if you need emissions readiness soon — photograph them first.
Pull the code yourself (disclosed)
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A reusable Bluetooth OBD-II scanner lets you read the code and freeze-frame data before authorizing “mystery” diagnostics. One option: BlueDriver Bluetooth Pro OBD-II scan tool (BlueDriver/Levanta affiliate). Any capable OBD-II reader is fine — this is not required to use Fair Auto Shops.
When to go to a shop
Request a structured EVAP diagnosis (cap seal, command tests, smoke test) before authorizing a canister. See gas cap and purge valve cost guides for related parts ranges.
Typical related repair costs (U.S. national averages)
These are related repairs shops may find after diagnosis — not a guaranteed bill for every P0440. Ranges exclude taxes, fees, diagnostics, and your location.
- $138–$150 national average for gas cap replacement (RepairPal; estimates last updated September 3, 2026; excludes taxes/fees and location; source). Labor $24–$36; parts about $114.
- $210–$251 national average for purge valve replacement (RepairPal; estimates last updated September 3, 2026; excludes taxes/fees and location; source). Labor $65–$95; parts $146–$156.
Start cheap: confirm the cap. Canister and major hose repairs cost more than these averages — demand smoke-test evidence.
Related cost guides: Gas Cap · Purge Valve
Questions to ask before you authorize work
Use questions before you authorize a repair and how to read a repair estimate. Watch for patterns in spotting upselling.
Find an honest independent shop
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FAQ
Will disconnecting the battery clear P0440 for good?
Clearing without a repair may turn the light off briefly and wipe readiness monitors. The fault returns if the leak or valve problem remains — and you may fail emissions for incomplete monitors.
More check-engine codes
P0420 · P0430 · P0300 · P0301 · P0171 · P0174 · P0455 · P0456 · P0442 · P0446 · P0128 · P0401 · P0133 · P0113 · P0506 · P0507 · P0700 · P0741 · P0011 · P0325 · P0340 · P0335 · P0101 · P0299 · P0135 · P0441 · P0010 · P0500 · P0121
Hub: How to read a check-engine code · Repair cost guides · Affiliate disclosure