P0442 Code: Small EVAP Leak Detected

What does P0442 mean?

P0442 stands for "Evaporative Emission System Leak Detected (Small Leak)." Your fuel tank constantly gives off gasoline vapor. The EVAP system catches that vapor in a charcoal canister and later lets the engine burn it. To make sure the system is sealed, the engine computer closes it off and checks whether it holds pressure or vacuum.

Identifix, a repair information provider, explains that P0442 means the computer found a leak bigger than its threshold but too small to count as a gross leak, about 0.040 inch in diameter. A leak anywhere from the fuel cap to the purge valve can set it ^[1].

That 0.040 inch size is not random. The U.S. EPA says federal OBD rules require cars to detect a leak of 0.040 inch or larger, while California's rules go down to 0.020 inch ^[2]. A P0442 leak is small, but it is exactly the size the federal rules were written to catch.

Is it safe to drive with P0442?

Yes, in most cases. Carista, a maker of diagnostic apps, rates P0442 as low severity: the check engine light comes on, you may notice a faint fuel smell now and then, and driving is unaffected ^[3].

Still, plan to fix it rather than live with it:

• Emissions inspection. EPA guidance says a car passes the OBD check only when no trouble code is commanding the light on and the required readiness monitors are set ^[4]. An active P0442 can fail you.
• A blind spot. With the light already on, a new fault will not get your attention the same way. If the light ever starts flashing, that is urgent; see our guide to a flashing check engine light.
• Strong fuel smell. A small vapor leak should not make the car reek of gasoline. If it does, or you see fuel on the ground, park it away from heat and have it inspected before driving more.

What causes P0442?

Here are the usual causes, cheapest and most common first. Haynes notes that while a loose fuel cap may trigger P0442, deeper inspection may reveal hose or seal problems ^[5].

Cause	What to look for	Who can check it
Loose or worn gas cap	Cap not clicked; seal cracked, flat, or hard	You
Filler neck seal or lip	Rust or nicks where the cap seals	You
Small split in an EVAP hose	Cracked rubber, loose clamp, unlatched connector	You for visible hoses; a shop for others
Purge valve leaking	Often paired with a purge code	Shop, or a scanner with active tests
Vent valve or solenoid leaking	Often paired with a vent code	Shop, or a scanner with active tests
Leaking charcoal canister	Usually no visible sign	Shop, with a smoke test
Tank pressure sensor, sending unit gasket, or tank	Found during a smoke test	Shop

Identifix lists the same group: loose cap, damaged hoses or fittings, purge or vent valves, the charcoal canister, a cracked or corroded filler neck, the tank pressure sensor, and a leaking tank or sending unit gasket ^[1]. Carista adds a worn O-ring on the fuel filler neck ^[3].

Some automakers have bulletins for EVAP leak codes. Identifix points to a Nissan bulletin, NTB13-097, covering P0442, P0455, and P0456 on many 2012 and newer models ^[1]. Ask a dealer or shop to check bulletins for your exact vehicle; our VIN decoder shows the model details you will need.

How do you diagnose P0442?

Go in order, from free to paid. Do not buy a purge valve, vent valve, or canister until a test shows the leak is there.

1. Scan for everything. Record all stored and pending codes and the freeze frame data. Identifix recommends reviewing all codes before deciding on a repair ^[1]. A purge or vent valve code next to P0442 narrows the search. New to scanners? Read how to use an OBD2 scanner.
2. Inspect the gas cap. Check that the seal is whole and soft and that the filler pipe lip is clean and smooth. Tighten it until it clicks. Carista says tightening or replacing the cap clears the code on a surprising number of vehicles ^[3].
3. Look at the hoses. With the engine off and cool, follow the EVAP lines you can see from the purge valve back toward the canister. Never crawl under a car held up only by a jack.
4. Drive normally and wait. Give the EVAP test time to run, as shown in the timeline below.
5. Smoke test. If the code returns, a shop fills the system with smoke to find the leak. Identifix warns that a clean smoke test does not always mean the system is sealed, since a leak can close under low pressure and open under vacuum ^[1].
6. Valve tests. A technician can command the purge and vent valves with a scan tool to check that each one seals.

How long until the light goes off after a fix?

Longer than most people expect. The EVAP leak test is not continuous. EPA guidance explains that the evaporative system monitor is one of the periodic monitors, which run only after a set of conditions are met, such as ambient temperature and driving conditions ^[4]. Under OBD II, the light goes off after three consecutive trips in which the problem does not come back ^[2].

You can clear the code with a scanner after a repair. Clearing P0442 does not fix the leak; if it is still there, the code comes back the next time the test runs. Clearing also resets readiness monitors, and EPA guidance names code clearing and battery disconnection as reasons a car shows up "not ready" for inspection ^[4].

How do you fix P0442, and what does it cost?

The fix follows the diagnosis: a gas cap, a hose or connector, a purge or vent valve, a canister, or a seal at the tank. We do not give dollar amounts because we could not find a reliable, current U.S. price source covering these repairs. The cost depends on:

• Which part leaks. A cap is a quick fix. Parts mounted near the tank take more labor.
• How long the search takes. Shops charge diagnostic time, and small leaks can be slow to pin down.
• Bulletins. A known fix for your model can shorten the search.
• Part fit. EVAP parts must seal exactly; a poor fit can bring the code back.

If you take the car to a shop, bring what you already know. It saves diagnostic time and keeps the shop from repeating checks you have done:

• The full list of codes, including pending ones, and the freeze frame data you saved.
• What you already tried, such as a new cap, and how many days you drove afterward.
• When the light came on. Right after a fill-up points toward the cap or filler neck.
• Any other signs, such as a fuel smell, trouble filling the tank, or rough running after refueling.
• Any other EVAP codes from the past, since a leak that keeps returning can be a different part each time.

Ask whether the shop will smoke test the system before replacing parts, and whether they checked for service bulletins on your model.

How is P0442 different from P0455 and P0456?

They come from the same test and differ only in leak size. P0456 is the smallest, about 0.020 inch, and P0455 is a large or gross leak ^[1]. If your scanner shows other codes too, look them up with our code lookup tool or the trouble code index.