# P0442: Evaporative Emission System Leak Detected (small leak) **Verdict:** Safe to drive Emissions - Generic OBD-II code, applies to all gasoline cars and light trucks sold in the US since 1996. - **Typical cost:** $20-$600 - **Urgency:** Keep driving - **Most likely:** Gas cap seal or small cracked EVAP hose - **DIY?:** Steps 1-2 ## Quick answer P0442 means the engine computer has found a small leak in the evaporative emission (EVAP) system, the sealed system that holds fuel vapor from the gas tank. The leak is roughly the size of a pinhole up to about 0.040 inch, so you probably will not smell anything. A worn gas cap seal, a cracked hose, or a leaking valve is the usual cause. ## What does P0442 mean? The EVAP system is a sealed set of parts that stores gasoline vapor instead of letting it escape: the gas cap, filler neck, tank, hoses, charcoal canister, purge valve, and vent valve. Because fuel vapor is a pollutant, the engine computer regularly checks this system for leaks. P0442 is the small-leak code, usually set for a leak about 0.040 inch across, roughly the size of a pinhole. A leak that small is rarely visible and seldom smells. To test, the computer closes the vent valve to seal the system, then uses engine vacuum, a small pump, or the natural pressure change as the tank cools to create pressure or vacuum. A fuel tank pressure sensor or a pump-current reading shows how quickly it bleeds off. If it leaks faster than the small-leak limit, P0442 sets. The test only runs under specific conditions, often after a long cool-down with a partly full tank, and on most cars the light comes on after two failed tests. ## What are the symptoms of P0442? - Check engine light on - Car drives normally - Failed emissions test - Occasionally a faint fuel smell ## What causes P0442? Ranked from most to least likely. Check them in this order: the cheap, common causes first. 1. **Worn or loose gas cap** (most common). The rubber seal on the gas cap can crack, flatten, or harden over time, and a cap that is not clicked tight leaks too. Because it is the easiest part to check, it is always the first suspect. A cap tester at a parts store or shop can check it quickly, and a new cap is inexpensive. 2. **Small crack in an EVAP hose or fitting** (common). Rubber hoses and plastic connectors between the tank, charcoal canister, and engine slowly crack from heat, ozone, and age. A tiny split or a loose quick-connect fitting is enough to set P0442. These leaks are usually too small to see without a smoke test, especially when they sit above the fuel tank. 3. **Leaking purge or vent valve** (common). The purge valve and vent valve must seal tightly while the computer runs its leak test. A valve that does not fully close, often from dirt, charcoal dust, or a worn seat, lets a little air in or out. Vent valves near the tank are exposed to water and road grime, which makes them likelier to leak. 4. **Leaking charcoal canister or filler neck** (less common). A hairline crack in the charcoal canister or rust pinholes in a steel filler neck can cause a slow leak. Filler neck rust is more common on older vehicles in states that salt their roads. Both are usually found by smoke testing, and the fix means replacing the damaged part rather than patching it. ## How do you diagnose P0442? 1. Inspect and tighten the gas cap, or test it with a cap pressure tester. 2. Clear the code and drive for several days. If it returns, the leak is elsewhere. 3. Have a shop perform a smoke test to locate the leak. 4. Test the vent and purge valves for proper sealing. ## How do you fix P0442, and what does it cost? | Fix | Typical cost | What it involves | | --- | --- | --- | | Replace gas cap | $20-$50 | Cheapest fix and often the right one. | | Smoke test and replace leaking hose | $150-$400 | Price includes finding the leak and replacing a hose or seal. | | Replace vent valve, purge valve, or canister | $150-$600 | Depends on which part fails the test and where it sits. | Full price breakdowns: [evap purge valve replacement cost](/cost/evap-purge-valve-replacement). ## Is it safe to drive with P0442? > **Safe to drive.** It is safe to drive. A small EVAP leak is mainly an emissions issue, though a strong fuel smell should be checked right away. ## Will P0442 fail an emissions test? P0442 with the check engine light on fails an OBD-based emissions test in most states. Some state programs also test the gas cap separately with a pressure tester, so a worn cap can fail twice. Clearing the code before testing resets the EVAP monitor, which is often the slowest to complete, so allow several days of driving first. ## After the repair: clearing P0442 After replacing the cap, hose, or valve, clear the code and drive normally for about a week. Many cars only run the small-leak test after an overnight cool-down, with fuel between about a quarter and three-quarters full. The repair worked when the EVAP monitor shows ready and no pending P0442 or P0456 appears on a scan tool. ## How to prevent P0442 - Tighten the gas cap until it clicks, and replace it if the rubber seal looks cracked or flattened. - Avoid topping off after the pump clicks, which can soak the canister and stress its seals. - Have the cap tested at a parts store or shop when it is several years old. - Ask for EVAP hoses near the tank to be inspected when the car is on a lift. - Wash winter road salt from under the car to slow rust on the filler neck and fittings. ## Codes often seen with P0442 - [P0455](/codes/p0455): Evaporative Emission System Leak Detected (large leak) - [P0456](/codes/p0456): Evaporative Emission System Leak Detected (very small leak) - [P0440](/codes/p0440): Evaporative Emission System - [P0446](/codes/p0446): Evaporative Emission System Vent Control Circuit ## Frequently asked questions ### Can I drive with a P0442 code? Yes, a small EVAP leak does not affect how the car drives or harm the engine. Fix it before your emissions test so you pass, and have it checked sooner if you notice a fuel smell. Leaving it alone also keeps the check engine light on, which can hide new problems. ### How long does it take for the light to go off after fixing P0442? It often takes several days to a week of normal driving, because the computer only runs the leak test under certain conditions. Many cars need an overnight cool-down and a fuel level between about a quarter and three-quarters full. Clearing the code with a scan tool turns the light off immediately. ### What is the difference between P0442 and P0455? P0442 is a small leak, while P0455 is a large leak such as a missing gas cap or a disconnected hose. Large leaks are usually easier to find because they show up quickly on a smoke test. Small leaks can hide in hose joints, valve seals, or the cap seal. ### How much does it cost to fix P0442? Most P0442 repairs cost $20 to $600 at an independent shop. A new gas cap is $20 to $50, a smoke test plus a replacement hose or seal is about $150 to $400, and a vent valve, purge valve, or canister runs $150 to $600 depending on location. ### Will P0442 make me fail an emissions test? Yes, P0442 will fail an OBD-based emissions test in most states while the check engine light is on. Clearing the code just before the test resets the EVAP monitor, which may then show not ready. Fix the leak and drive for several days before testing. ### Can I fix P0442 myself? You can often fix P0442 yourself if the gas cap is the cause, since a new cap takes seconds to install. Visible cracked hoses near the engine are also manageable. Hidden leaks near the tank usually need a shop smoke test, because pinhole leaks are very hard to find by eye. ### Can a gas cap cause P0442? Yes, a worn or loose gas cap is the most common cause of P0442. The rubber seal hardens and cracks with age, letting a small amount of vapor escape. Replace it with a cap made for your vehicle, then drive normally for several days to see if the code returns. ### How small is a small EVAP leak? A small leak for P0442 is about 0.040 inch across on most vehicles, roughly the size of a pinhole. Many newer cars also test for even smaller leaks of about 0.020 inch, which set P0456 instead. Leaks this small rarely produce a fuel smell, so a smoke test is usually needed. ### Why does P0442 come and go? P0442 can come and go because the leak test depends on temperature, fuel level, and how much vapor the fuel is making. A borderline leak, such as a cap seal that is just starting to harden, may pass some tests and fail others. If it keeps returning, have the system smoke tested. ### Can a smoke test find a P0442 leak? Yes, a smoke test is the standard way to find small EVAP leaks. The shop seals the system, fills it with low-pressure smoke, and watches for wisps at hoses, valves, the canister, and the filler neck. It usually costs about $100 to $180, and it saves replacing parts by guesswork. ## Sources - [SAE J2012: Diagnostic Trouble Code Definitions](https://www.sae.org/standards/content/j2012_201812/) - [EPA: On-Board Diagnostics (OBD)](https://www.epa.gov/state-and-local-transportation/vehicle-emissions-board-diagnostics-obd) ## Other emissions codes - [P0430 Catalyst System Efficiency Below Threshold (Bank 2)](https://diagxcar.com/codes/p0430) - [P0431 Warm Up Catalyst Efficiency Below Threshold (Bank 2)](https://diagxcar.com/codes/p0431) - [P0440 Evaporative Emission System](https://diagxcar.com/codes/p0440) - [P0441 Evaporative Emission System Incorrect Purge Flow](https://diagxcar.com/codes/p0441) - [P0443 Evaporative Emission System Purge Control Valve "A" Circuit](https://diagxcar.com/codes/p0443) - [P0446 Evaporative Emission System Vent Control Circuit](https://diagxcar.com/codes/p0446) - [P0449 Evaporative Emission System Vent Valve/Solenoid Circuit](https://diagxcar.com/codes/p0449) - [P0451 Evaporative Emission System Pressure Sensor/Switch "A" Circuit Range/Performance](https://diagxcar.com/codes/p0451) - [P0452 Evaporative Emission System Pressure Sensor/Switch "A" Circuit Low](https://diagxcar.com/codes/p0452) - [P0455 Evaporative Emission System Leak Detected (large leak)](https://diagxcar.com/codes/p0455) - [P0456 Evaporative Emission System Leak Detected (very small leak)](https://diagxcar.com/codes/p0456) - [P0457 Evaporative Emission System Leak Detected (fuel cap loose/off)](https://diagxcar.com/codes/p0457) - [P0498 Evaporative Emission System Vent Valve Control Circuit Low](https://diagxcar.com/codes/p0498) ## Symptoms - [Why does my car smell like gas?](https://diagxcar.com/symptoms/car-smells-like-gas) ## Repair costs - [EVAP purge valve replacement cost](https://diagxcar.com/cost/evap-purge-valve-replacement): $120-$350 ## Warning lights linked to this - [Check engine light](https://diagxcar.com/warning-lights/check-engine) ## Terms explained - [What is EVAP system?](https://diagxcar.com/glossary/evap-system) --- Source page: https://diagxcar.com/codes/p0442 Updated: 2026-11-03 General information, not a substitute for a qualified mechanic.