P0442: There is a small leak in your fuel vapor system

Evaporative Emission Control System Leak Detected (Small Leak)

What it means

Your car catches fuel vapors in a sealed system and stores them in a charcoal canister instead of letting them escape. The computer runs a self-test, seals the system, and watches whether it holds pressure or vacuum. When it leaks down faster than allowed, this code sets. A small leak is about a 0.04 inch hole, so you usually cannot see it. This is an emissions code, not an engine problem. Here is the trap most people fall into: they fix it, the light stays on the next morning, and they assume the fix failed and start buying parts. The light does not clear right away. The test only reruns under certain driving, so it can take several days.

Common causes

1. Gas cap not sealing, plus the neck it seats againstThe number one cause. Loose, worn O-ring, aftermarket, or a rusted filler neck. A perfect cap cannot seal against a corroded neck.
2. Cracked, split, or disconnected vapor hose or lineWhat a smoke test usually finds when it is not the cap. Includes rusted metal lines and rotted filler necks on older, rust-belt cars.
3. EVAP vent valve or solenoid not sealingDirt, water, or corrosion keeps it from closing during the test. A known leaking pattern on 2011 to 2013 GM vehicles.
4. Purge valve or solenoid leaking or not sealingCommon on Mercedes, Hyundai, Nissan, Ford, and Mazda. A bit less common than the vent valve for this small-leak code.
5. Cracked charcoal canister or leaking tank sealsIncludes the vent O-ring and the fuel pump or sending-unit gasket. Real but less frequent, and the priciest of the common fixes.

What the fix could involve

From the cheaper fix to the bigger one. Prices depend on your car, your area and the shop, so ask for a written quote that names the part and the labor before you approve it.

• Gas cap (use OEM)
• EVAP smoke test to find the leak
• Vapor hose or line replacement
• Purge or vent valve/solenoid replacement
• Fuel tank pressure sensor replacement
• Charcoal canister replacement

Symptoms

• Check engine light on, often the only symptom
• No noticeable change in how the car drives
• A faint gas smell sometimes, especially after filling up
• Slightly worse fuel economy over time
• Failed emissions or smog inspection while the code is set

What to do next

Start with the cheapest check before you pay anyone. Remove the gas cap and reseat it firmly until it clicks several times. Look at its O-ring for dryness or cracks. Then do the step almost everyone skips: check the filler-neck surface the cap seats against for rust or a trapped cap tether. A new cap cannot seal against a corroded neck. The car reruns its own leak test over about a week of your usual trips. If the code comes back, pay for a smoke test before buying any part. Do not parts-cannon purge and vent solenoids on guesswork when a smoke test finds a rusted line or cracked canister in minutes.

Lewis reads P0442 alongside any related EVAP codes, stored or pending, so you can see whether the leak is the only fault and whether it comes back after a fix. Get Lewis on the App Store or Google Play.

Related codes

• P0440
• P0441
• P0443
• P0446
• P0455
• P0456
• P0457

FAQ

Can I fix P0442 by just tightening my gas cap?

Sometimes, yes. A loose or worn cap is the most common cause. Reseat it until it clicks several times and check the O-ring. Also check the filler neck it seals against for rust. But the light will not clear right away, so give it about a week of driving before you decide the cap was not the fix.

How long until the check engine light turns off after fixing the leak?

Not right away. The EVAP self-test only reruns under specific driving conditions, so it can take several days of normal driving to clear on its own. People often assume the fix failed the next morning and start buying parts they do not need. Give it a week first.

Is it safe to keep driving with a P0442 code?

It is an emissions leak, not a braking or steering fault, and most cars feel normal. That is not a reason to leave it. You will fail emissions, fuel economy can slip, and long neglect can contribute to converter damage. Get it checked within a couple of weeks, and right away if you smell strong gas.