Cause of P0440 on 1999 Subaru Legacy Outback

Question

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?

Answer 1

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.