P0442 Small EVAP Leak Detected

What it means

Your fuel system is sealed so fuel vapor is stored and burned instead of escaping. The computer tests the seal now and then by holding a small pressure or vacuum on the tank. P0442 means the seal lost a little too fast: a small leak. It has no effect on how the engine runs.

The technical version

The EVAP monitor closes the vent valve, uses the purge valve or a pump to pull or push a small vacuum or pressure, and watches the tank pressure sensor. A slow decay is a small leak (P0442, or P0456 for a very small one); no hold at all is a large leak (P0455). The test needs specific conditions, often a cold start and a fuel level between about a quarter and three quarters, so it does not run on every drive.

Official name: Evaporative Emission Control System Leak Detected (small leak).

Symptoms

• Usually none apart from the light.
• Sometimes a faint fuel smell near the car.

Causes, most likely first

How likely is our ranking from repair data and common practice, not a published rate.

What the live data shows

There is no single live reading that shows a small leak. The useful ones are fuel tank pressure (where fitted) and EVAP purge percentage. The real check is the EVAP readiness monitor: after a fix, it should show complete within a few days of normal driving, and the code should not return.

What to check first, in order

1. Tighten the gas cap until it clicks, or replace it if the seal is worn.

   It is the most common cause and the cheapest fix.

   What the data shows: No reading needed.

   Cost: $138-$150 at a shop (Gas cap replacement, RepairPal)

2. Clear the code and drive normally for a few days.

   The EVAP test needs certain conditions to run.

   What the data shows: Watch the EVAP readiness monitor change to complete.

   Cost: no cost if you have a scanner

3. If it comes back, have a smoke test done.

   Smoke shows small cracks you cannot see.

   What the data shows: Not a scanner step.

   Cost: $61-$90 at a shop (Emission system diagnosis (shop), RepairPal)

4. Replace the part the smoke test finds: hose, purge valve, vent valve or canister.

   Fix only what the test shows.

   What the data shows: EVAP monitor completes and the code stays away.

   Cost: $210-$251 at a shop (EVAP purge valve replacement, RepairPal)

Is it safe to drive?

Drive normally - check soon

Yes. It does not affect how the engine runs.

This is an emissions fault, not a mechanical one. The car drives the same. You may notice a faint fuel smell, and the car will fail an emissions test while the light is on.

Stop driving and get help if

• You smell strong fuel or see fuel dripping: that is a real leak, not vapor.

What it costs

National averages for the full job at a shop, parts and labor, from RepairPal (updated September 3, 2026). Your price depends on the car and the area. Many of the first checks on this page cost nothing with a scanner. The EVAP purge valve was CarMD's number 6 check engine repair in 2025, at an average of $172. CarMD averages come from a different method (repairs reported by its users), so they can sit below RepairPal's shop estimates.

Sources for the notes: CarMD 2026 Vehicle Health Index (press release, April 22, 2026).

Can I clear it? Will it come back?

Clearing resets the EVAP monitor, which can take several days to run again. Do not clear it right before an emissions test.

Will it fail an emissions test?

Yes, while the check engine light is on, most OBD emissions tests fail the car, and an incomplete EVAP monitor after clearing can also cause a fail or a 'not ready' result.

Carmaker notes

Service bulletins and warranty extensions that name this code. Ask a dealer to check your VIN.

• GM 2007-2010 Escalade, Avalanche, Suburban 1500, Tahoe, Yukon

  GM bulletin 09-06-04-028D (April 2014) links P0442, P0446, P0455 and P0449 to water and corrosion at the EVAP vent (CVS) valve.

  GM 09-06-04-028D via NHTSA static.nhtsa.gov

• Hyundai certain 2011-2015 Sonata Hybrid

  Hyundai bulletin 21-FL-002H (June 2021): salt deposits in the leak-detection sensor can set P0442, P0455 or P0456.

  Hyundai TSB 21-FL-002H via NHTSA static.nhtsa.gov

Related codes

Also related, no guide yet: P0456, P0457, P0441, P0446.

Questions people ask

Can a gas cap cause P0442?

Yes. A worn or loose gas cap is the most common cause. Tighten it until it clicks or replace it.

How long after fixing does P0442 clear?

The light goes out after the EVAP test passes, which can take several days of normal driving.

Is P0442 serious?

No. It does not affect how the car runs, but it fails emissions tests.

Sources

1. RepairPal: P0442 code page repairpal.com
2. RepairPal: Emission system diagnosis (shop) (updated September 3, 2026) repairpal.com
3. RepairPal: Gas cap replacement (updated September 3, 2026) repairpal.com
4. RepairPal: EVAP purge valve replacement (updated September 3, 2026) repairpal.com
5. RepairPal: EVAP canister replacement (updated September 3, 2026) repairpal.com
6. CarMD 2026 Vehicle Health Index (press release, April 22, 2026) prnewswire.com
7. GM 09-06-04-028D via NHTSA static.nhtsa.gov
8. Hyundai TSB 21-FL-002H via NHTSA static.nhtsa.gov
9. Texas DPS emissions testing FAQ dps.texas.gov
10. Arizona myazcar.com: OBD and the check engine light myazcar.com