P0442: EVAP System Leak Detected (Small Leak)
P0442 means the car's fuel vapor (EVAP) system has found a small leak somewhere between the fuel tank and the engine. It is not a safety emergency and does not change how the car drives, but it turns on the check engine light and can cause a failed emissions test.
You can keep driving
The code does not cause limp mode or affect how the car drives, so normal driving is fine. The leak lets fuel vapor escape, so you may notice a slight fuel smell, and the car will not pass an emissions inspection until it is fixed.
What it means
The EVAP system catches fuel vapor from the tank and stores it in a charcoal canister. A purge valve then lets the engine draw that vapor off and burn it, and a vent valve opens the canister to fresh air when needed. The engine computer tests the system for leaks, and P0442 is set when it finds a small one. What counts as small depends on the manufacturer. Ford, for example, looks for a leak of about 0.040 in (1 mm) with the engine running, while GM uses the natural pressure change after the engine is switched off and averages several tests. VW and Audi use a pump that compares against a reference leak. The most common cause is a worn or loose fuel cap.
Likely causes
- Fuel cap seal worn, wrong or not clicked inVery likely
A cap that is worn, the wrong type or not tightened until it clicks lets vapor out of the tank, and this is the most common cause.
- Cracked or porous EVAP hoses or leaking connectionsVery likely
Old rubber and plastic lines can crack or loosen at their fittings and leak vapor.
- Purge or vent valve does not sealPossible
If either valve fails to close fully, the system cannot hold pressure or vacuum during the test.
- Leak detection pump itself leaking (VW/Audi)Possible
On cars that use this pump to test the system, a leak inside the pump causes the same result.
- Filler neck corroded, tank or sender seal leakingLess likely
Rust on the filler neck or a bad seal where the fuel level sender enters the tank can leak, but this is less common.
What you may notice
- Check engine light on
- Possibly a slight fuel smell
- Readiness or emission inspection not passed
- No change in driving
What to check, cheapest first
- 1Remove the fuel cap, inspect the seal for cracks or wear, and refit it until it clicks. Make sure it is the correct cap for the car. · you can do it
- 2Replace the cap if the seal looks worn or damaged, then clear the code and drive normally so the system can retest itself (a drive cycle is required). · you can do it
- 3Look over the visible EVAP hoses and connections near the engine, canister and filler neck for cracks, loose fittings or disconnected lines. · you can do it
- 4Read the stored code and freeze-frame data with a scan tool, and check for related codes such as P0455 or P0456. · mechanic
- 5Run a smoke test, which pushes harmless smoke into the EVAP system so the leak shows where smoke escapes. · mechanic
- 6Test the purge valve, vent valve and (on VW/Audi) the leak detection pump for sealing, and inspect the filler neck and tank seals. · mechanic
Related codes
Frequently asked questions
Can I keep driving with a P0442 code?+
Yes. The code does not affect how the car drives. Have it fixed so the check engine light is not hiding other problems and the car can pass an emissions test.
Can a loose or bad gas cap cause P0442?+
Yes, it is the most common cause. A worn, wrong or not fully clicked cap lets vapor escape. Check or replace the cap first.
Will P0442 pass an emissions test?+
No. The code is emissions-relevant and turns on the check engine light, so the car will not pass inspection until the leak is fixed and the system has completed its retest.
How hard is it to fix?+
Difficulty is medium and many owners can do the work. Time ranges from about 0.2 hours for a gas cap to around 3 hours for harder repairs.
Written with the help of AI from the public OBDex definition (CC0). Each make may use the code differently. Updated: 2026-11-10