P0442: a small leak in your fuel vapor system

What the computer saw

The computer seals the fuel vapor system and watches whether it holds. P0442 means it found a small leak, roughly the size of a pinhole. It is an emissions fault, and it is usually found with a smoke test.

Likely causes, most common first

1. A worn gas cap seal. A cap that closes but no longer seals fully is a common cause.
2. A small crack in an EVAP hose. Rubber hoses harden and crack with age and heat.
3. A purge or vent valve that does not seal. A valve that leaks slightly when closed.
4. A rusted filler neck or a cracked canister. More common on older cars and in places that salt their roads.

What you can note yourself

• Look at the gas cap's rubber seal for cracks, and tighten the cap until it clicks.
• Note whether the light came on soon after a fill-up.
• Allow several days of normal driving after any fix for the computer to rerun its test.

What to tell the shop

• All the codes, and whether P0455 or P0456 came with it.
• Whether you replaced the gas cap, and when.
• Ask for a smoke test to find the leak before parts are replaced.

This page gives no verdict on whether a car is safe to drive; a mechanic can.

Related pages

• P0442 and P0455 together: a small and a large fuel vapor leak
• P0455: a large leak in your fuel vapor system
• P0442 came back after a new gas cap