Motor Vehicle Maintenance & Repair Stack Exchange is a question and answer site for mechanics and DIY enthusiast owners of cars, trucks, and motorcycles. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

I get a P0440 code on my Outback on almost every highway trip over 5 miles. Is this caused by the leak in the gas tank or could it be something else?

share|improve this question
up vote 4 down vote accepted

This can be caused by a number of things, including:

  • Leak in the fuel tank (loose cap)
  • Leaking evaporator canister (plastic housing in engine compartment or under vehicle, also known as charcoal canister)
  • Plugged evaporator canister - there is a tube that is open to the air that can become plugged
  • Malfunctioning purge valve - valve itself is faulty or wiring to the valve is faulty
  • Malfunctioning sensor - The whole system may be working just fine, but the sensor that monitors the system may be faulty. It checks for pressure or vacuum at key times while driving to make a guess about how well everything is working.

So, everything from a $5 gas cap (free, if it's just loose), to a very expensive fuel tank can cause this one.

share|improve this answer
Good to know. I know the tank definitely has a leak around the 3/4 mark so that's likely the cause then. – travis Mar 7 '11 at 23:33
Hey, I think I have the same problem, Subaru imprezza, though. – Kzqai Mar 7 '11 at 23:34

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.