P0442: Evaporative Emission System Leak Detected (Small Leak)
Key takeaways
- P0442 means the fuel vapor system held pressure or vacuum, but lost it slowly, which points to a small crack, a tired seal or a cap that is not sealing.
- It is safe to drive; the engine runs normally, but most emissions tests will fail with the light on.
- Start with the gas cap seal, then a smoke test, because small leaks are hard to find by eye.
- Most fixes cost $15-$350; a charcoal canister or filler neck is the expensive end at up to about $800.
What P0442 means
Your car found a small leak in the system that traps gasoline vapor from the tank. The scanner name is “Evaporative Emission System Leak Detected (Small Leak)”. The EVAP system stores tank vapor in a charcoal canister so the engine can burn it later. To test it, the computer closes the vent valve, pulls a vacuum or applies a small pressure, and watches how fast it bleeds off. If it holds at first but drifts too quickly, it sets P0442. Emissions rules require leak detection down to openings of 0.040 inch and 0.020 inch, so the leak can be smaller than a pinhead. That is why a small leak rarely shows up as a smell or a visible crack. The test runs in the background, so the light can appear days after whatever caused the leak.
Is it safe to drive?
Yes. P0442 has no effect on how the engine runs. You lose a small amount of fuel vapor, you will likely fail an emissions test that reads the OBD port, and the lit light can hide a new code. There is no rush measured in miles, but fixing it within a few weeks keeps the light useful.
The answer changes if you smell raw gasoline or see wet spots under the tank. That is liquid fuel, not a vapor leak, and it needs a look the same day.
Causes, ranked
| Cause | How you confirm it | Typical cost (US independent shop, 2026) |
|---|---|---|
| Gas cap seal hardened or cracked | Seal is flat, cracked or dry; code clears after a new cap | $0 to tighten, $15–$40 new |
| Small crack in an EVAP hose or connector | Smoke test shows a thin wisp at the hose | $100–$300 |
| Vent valve or purge valve not sealing | Scan tool command test, valve holds no vacuum | $120–$350 |
| Filler neck rust or seal leak | Smoke at the filler area | $250–$600 |
| Charcoal canister cracked | Smoke at the canister body | $300–$800 |
What to check first
- Check the gas cap. Tighten until it clicks and inspect the seal. With a small leak, a worn seal is a common answer. Our loose gas cap guide walks through it.
- Clear it and drive. For EVAP codes this is a fair test. Give it a week of normal use with the tank between a quarter and three-quarters full.
- Smoke test. If the code returns, this is the step that finds small leaks. It usually costs $100–$200, and a good shop shows you where the smoke comes out.
- Replace only the part the smoke points to. Hoses and valves near the tank and canister are the usual spots.
- Check bulletins. Nissan and Infiniti publish EVAP leak guidance for their 2012-and-newer models. GM has bulletins for 2019–2023 Silverado and Sierra trucks where dust gets into the canister and sets P0442 along with other EVAP codes.
What it costs
The cheap outcome is a new cap, $15–$40. The common outcome is a hose or valve for $100–$350 plus a smoke test. The expensive outcome is a canister or filler neck, up to about $800. Because small leaks are hard to see, paying for the smoke test first is almost always cheaper than replacing parts in turn. If you want help reading the shop’s findings, ask our AI mechanic.
Related codes
P0442 often travels with P0455 (large leak) and P0456 (very small leak), depending on how the leak changes. Valve circuit codes like P0441, P0440 and P0446 point to the purge or vent side. If the light goes on and off between tests, see check engine light comes on and off.
What owners report to NHTSA
53 complaints filed with NHTSA mention P0442, 30 of them since 2015, across 39 different models. The component owners most often filed it under: fuel/propulsion system.
Most-reported models
| Vehicle | Complaints | Model years reported |
|---|---|---|
| CHEVROLET TRAILBLAZER | 5 | 2003, 2004 |
| GMC ENVOY | 3 | 2003, 2004 |
| CHEVROLET CORVETTE | 3 | 2009, 2011, 2013 |
Manufacturer service bulletins that name P0442
192 technical service bulletins and manufacturer communications filed with NHTSA mention P0442, from 21 makes. A bulletin means the manufacturer has documented a known cause or a fix procedure for that model. Examples:
- INFINITI INFINITI, bulletin 10183904: 2012 AND NEWER INFINITI VEHICLES; EVAP LEAK DTC P0442, P0455, P0456 INFORMATION This bulletin has been amended. See AMENDMENT HISTORY on the last page. Please discard previous versions of this bulletin.
- NISSAN NISSAN, bulletin 10184003: 2012 AND NEWER NISSAN VEHICLES; EVAP LEAK DTC P0442, P0455, P0456 INFORMATION This bulletin has been amended. See AMENDMENT HISTORY on the last page. Please discard previous versions of this bulletin.
- NISSAN TITAN (2012, 2013, 2014, 2015), bulletin 10208948: EVAP LEAK DTC P0442, P0455, P0456 INFORMATION This bulletin has been amended. See AMENDMENT HISTORY on the last page. Please discard previous versions of this bulletin.
- GMC SIERRA 2500 (2020, 2021, 2022, 2023), bulletin 11010573: This technical bulletin provides repair information to correct a customer concern of Evaporative DTCs P0442, P0446, P0455 or P0449, Caused by Dust Intrusion into the Evaporative Canister.
- CHEVROLET SILVERADO 3500 (2020, 2021, 2022, 2023), bulletin 11010573: This technical bulletin provides repair information to correct a customer concern of Evaporative DTCs P0442, P0446, P0455 or P0449, Caused by Dust Intrusion into the Evaporative Canister.
- GMC SIERRA 3500 (2020, 2021, 2022, 2023), bulletin 10239087: This technical bulletin provides repair information to correct a customer concern of Evaporative DTCs P0442, P0446, P0455 or P0449, Caused by Dust Intrusion into the Evaporative Canister.
Sources: NHTSA Office of Defects Investigation complaint database and manufacturer communications file, snapshots September 2026. A complaint or bulletin that mentions a code is a report about that vehicle, not a statement that the code has one cause.
Frequently asked questions
Can a gas cap cause P0442?
Yes. A cap that clicks shut but has a hardened or cracked seal can leak just enough to set a small-leak code. A new cap is cheap, so it is a reasonable first step even if the old one looks fine.
Why does P0442 keep coming back after I clear it?
Clearing the code does not fix the leak. The computer reruns the test every few days under the right conditions, usually after the car sits cold with a partly filled tank, and it sets the code again when the leak is still there.
What is the difference between P0442 and P0456?
Both are small leaks. Many cars use P0442 for an opening around 0.040 inch and P0456 for the smallest ones, around 0.020 inch. The fix list is the same; the smaller the leak, the more a smoke test matters.
Will P0442 hurt my engine?
No. The EVAP system only handles fuel vapor from the tank, so a small leak does not affect how the engine runs. Fix it for the emissions test and so the check engine light can warn you about the next problem.
References
- NHTSA Office of Defects Investigation — complaint flat files (snapshot 2026-09-23)
- NHTSA — manufacturer communications / technical service bulletin flat files
- 13 CCR 1968.2 — California OBD II requirements, evaporative system monitoring (e)(4), Cornell LII
- EPA, Do You Drive a 1996 or Newer Car or Light Truck? OBD consumer brochure, EPA420-F-02-016 (2021 archive)