Can I drive with P0442?

Yes. P0442 is an emissions-system fault with no effect on drivability or safety. The car will run normally. You may fail an emissions test. Address it when convenient.

I tightened the gas cap but the code came back. Now what?

Next step: a smoke test at a shop. A technician pressurizes the EVAP system with inert smoke and looks for plumes at joints, hoses, and the canister. It typically takes 30–45 minutes and costs $75–$120 to find the leak location. Then you know exactly what to replace rather than guessing.

What's the difference between P0442 and P0455?

P0442 = small EVAP leak (the system detected a leak below a small threshold). P0455 = large EVAP leak (a much bigger leak that is usually more obvious — often a gas cap left off entirely or a completely disconnected hose). Both start with the gas cap, but P0455 is usually something more dramatic.

How long can I drive with P0442?

Indefinitely from a mechanical standpoint — it won't cause engine damage. But if your state requires emissions testing, the code will cause a fail. Most states require the car to complete several drive cycles with the EVAP monitors passing before the car will pass inspection even after a repair.

P0442low severityGenerally driveable

P0442 Code: Evaporative Emission System Leak Detected (Small Leak)

What it means in plain English

Your fuel tank is sealed — gasoline vapors can't just escape into the air because they're smog-forming and toxic. The evaporative emission (EVAP) system captures those vapors and feeds them into the engine to be burned. P0442 means the ECM has run a self-test on this sealed system and found a small leak — air is getting in somewhere it shouldn't be. The most common cause is literally just a loose gas cap.

Most likely causes — ranked

#1 Loose, cracked, or improperly seated gas cap

most likely

Fix: Remove the gas cap completely and reinstall it, turning until you hear it click at least once (or until it feels firmly seated on capless systems). Clear the code with an OBD2 scanner and drive normally for one or two drive cycles. If the code does not return, the gas cap was the culprit. If you haven't replaced the cap in several years, a new one costs $10–$25 and is worth it.

DIY ~$15Shop ~$30

#2 EVAP purge control valve (purge solenoid) leaking or stuck open

likely

Fix: The purge valve opens during engine operation to pull stored vapors from the charcoal canister into the intake manifold. If it leaks when closed, the system fails its seal test and sets P0442. On most vehicles the purge valve is located on the intake manifold or vapor canister hose and can be tested for resistance with a multimeter (typically 14–30 ohms closed). Replace if out of spec or if it clicks erratically.

DIY ~$20Shop ~$160

evap purge valve repair guide

#3 Cracked or disconnected EVAP hose

possible

Fix: The EVAP system uses rubber and plastic hoses to connect the gas tank, charcoal canister, purge valve, and intake. These hoses age and crack, especially under the hood where heat cycles are extreme. A visual inspection under the hood and under the car (near the fuel tank) may reveal obvious cracks. A shop's smoke test pumps smoke through the EVAP system and lets technicians pinpoint even small leaks.

DIY ~$15Shop ~$200

#4 Leaking charcoal (vapor) canister

possible

Fix: The charcoal canister sits near the fuel tank and adsorbs fuel vapors when the engine is off. If the canister body cracks or a fitting breaks, the system leaks. This is typically found via a shop smoke test. The canister is usually accessible from underneath the rear of the vehicle without major disassembly.

DIY ~$50Shop ~$300

Get a FREE OBD2 scan first — no purchase required

AutoZone, O'Reilly Auto Parts, and Advance Auto Parts all scan your car's computer for free. Walk in, they plug in a scanner, you get a code in under 2 minutes. Then come back here and look up that code at eli5cars.com/obd2 for the plain-English explanation.

Pro tip: Take a photo of the code before they clear it.

P0442 Code: Evaporative Emission System Leak Detected (Small Leak)

Most likely causes — ranked

Get a FREE OBD2 scan first — no purchase required

Frequently asked questions