P0442 code: Evaporative emission system small leak detected (0.040 in)

What P0442 means

Your fuel tank gives off gasoline vapor. The EVAP system traps that vapor in a charcoal canister and later burns it in the engine through the purge valve, instead of venting it to the air. To make sure the system is sealed, the powertrain control module (PCM) runs a leak test. On many vehicles it seals the system with the vent valve and watches pressure or vacuum with a fuel tank pressure sensor. Other designs use a leak detection pump or a natural vacuum leak detection switch.

P0442 is the generic SAE code for Evaporative Emission System Leak Detected (small leak). Small usually means a leak about the size of a 0.040 inch hole. A larger leak sets P0455 and a very small one (0.020 inch) sets P0456. The test only runs under certain conditions, such as a cold start after the car has sat for several hours with a fuel level in a mid range, so the code can take days to come back after you clear it.

Symptoms of P0442

Most cars with P0442 drive normally. The check engine light is often the only sign. You may also notice:

• Check engine light on, usually steady, not flashing
• A faint fuel smell near the car, especially near the filler or rear of the vehicle
• A 'Check gas cap' or 'Check fuel cap' message on some models
• Failed emissions or state inspection because of the stored code or incomplete EVAP monitor

Note.If you smell strong raw fuel or see fuel dripping, that is not a typical P0442 and should be checked right away. Do not use open flames or create sparks near a fuel leak.

Common causes of P0442

Start at the top of this table. The gas cap and visible hoses are quick and cheap to check, so rule them out before you buy valves or a canister.

How to diagnose P0442

A basic code reader tells you the code. A scanner with live data, freeze frame and, ideally, bidirectional controls makes the EVAP diagnosis much easier. See our guide to bidirectional scan tools if you are not sure what yours can do.

1. 1

   Read all codes and save the freeze frame data. Note any other EVAP codes such as P0446, P0455 or P0456.

2. 2

   Remove the gas cap and inspect the seal. Clean the filler neck lip. Reinstall the cap until it clicks, or replace it if the seal is cracked or the cap is not the right part.

3. 3

   Inspect every EVAP hose you can reach: the purge line near the intake and the lines near the canister and tank. Look for cracks, chafing and loose connections.

4. 4

   With a bidirectional scan tool, command the purge valve and vent valve and listen for them to click. Many tools can also run an EVAP leak test or seal the system for testing.

5. 5

   Smoke test the system. A smoke machine pushes visible smoke into the EVAP system at low pressure; the smoke shows exactly where the leak is. Many shops do this as a standard step.

6. 6

   Repair the leak, clear the code, and drive normally. Check the EVAP monitor status over the next several days to confirm the test passes.

See bidirectional scan tools →

How to fix P0442

Fix the cause you found, not the code. If the gas cap was loose or worn, a new cap is often the whole repair. If a smoke test points to a hose, valve or canister, replace that part and recheck. After the repair, clear the check engine light and let the car complete a drive cycle. The EVAP monitor is often the slowest to run, so give it several days of normal driving with cold starts.

Clearing the code without a repair only hides it. The EVAP monitor will show as not ready, and many inspection stations will fail or reject the car until it is ready. Check status in readiness monitors.

Can you drive with P0442?

Yes, in most cases. P0442 does not affect how the engine runs and is not likely to cause damage. The downsides are fuel vapor escaping into the air, a possible fuel smell, a failed emissions test, and a lit check engine light that could hide a new, more serious code. Fix it when convenient, and check the gas cap first since it costs nothing to look.

Related codes

EVAP codes often appear together. P0455 is a large leak, P0456 is a very small leak, P0446 points to the vent control circuit, P0449 is the vent valve solenoid circuit, and P0496 is purge flow when it should not be flowing. If you just filled up and the light came on, read check engine light after getting gas. You can look up any other code with our code decoder.

Frequently asked questions

Can a gas cap really cause P0442? Yes. A cap that is loose, worn, cross-threaded or the wrong part is one of the most common causes. Tighten it until it clicks or replace it, then give the EVAP monitor several days to rerun before deciding it did not work.

How long after fixing P0442 will the light go off? If you clear the code, the light goes off right away. If you do not clear it, the PCM usually turns the light off after the EVAP test passes on several consecutive drive cycles. That can take days because the test needs specific conditions.

What is the difference between P0442 and P0455? Both are EVAP leaks. P0442 is a small leak, around 0.040 inch. P0455 is a large leak or no seal at all, often a missing cap or a disconnected hose.

Do I need a smoke machine? Not always. Many P0442 cases end with a gas cap or an obvious cracked hose. If those check out, a smoke test is the fastest way to find a small leak, and a shop can do it if you do not own one. A good OBD2 scanner helps you confirm the repair.