Repair cost
$90–$600
DIY from $5
DIY difficulty
Easy
If you do it yourself
Urgency
Within a month
Before bigger damage
Common symptoms
- Check engine light on
- No change in how the car drives
- Occasional faint fuel smell
- Will fail an emissions test
Common causes, ranked by likelihood
Based on typical diagnoses for P0440. Work from the most likely cause down before replacing expensive parts.
Loose, damaged, or missing gas cap 45%
Cracked or disconnected EVAP hose 25%
Faulty purge or vent valve 20%
Leaking charcoal canister 10%
How to diagnose it
- Check the gas cap first — make sure it's the correct cap, undamaged, and clicked tight. Then clear the code and drive a few cycles.
- Inspect EVAP hoses and connections under the hood and near the tank for cracks or disconnects.
- Test the purge and vent valves for proper operation.
- If needed, have a smoke test performed to pinpoint the leak.
DIY vs shop cost
Shop
$90–$600
Parts + labour at an independent shop.
DIY can save up to $30
Make-specific notes
Toyota
Frequently just the gas cap or a sticking vent valve; try a genuine cap before deeper diagnosis.
P0440 questions, answered
Is it safe to drive with P0440?
Yes. P0440 is an emissions fault that doesn't affect safety or drivability. It's worth fixing because it will fail an emissions test and may slightly waste fuel vapor.
Can a gas cap really cause P0440?
Yes — a loose, cracked, or wrong gas cap is one of the most common causes. Always tighten or replace the cap and clear the code before chasing anything else.