EVAP System Small Leak Detected
Fuel vapor system has a small leak — usually under 0.040 inches. Often the gas cap.
What it means (plain English)
Modern vehicles seal the fuel tank to keep gasoline vapors from venting to atmosphere. The EVAP system pulls a small vacuum (or pressurizes, depending on system) and watches for leaks. P0442 means it detected one — small enough that you won't smell anything, but big enough to fail the test. Number one cause: loose or worn gas cap.
What the computer is actually seeing
EVAP monitor pulled vacuum on the sealed system and saw it bleed off faster than allowed for a 0.040" leak threshold.
What a healthy reading looks like
Fuel tank pressure sensor should hold its commanded value during the EVAP test (varies by system, typically -7 to -10 inH2O).
Guided diagnostic — the DiagCoach way
Don't just throw parts at it. Walk through these in order — each step tells you whether to keep going or stop and fix what you found.
- 1Check the gas cap first. Tighten until 3 clicks. Inspect the seal.
- 2Clear the code and drive 2 drive cycles. If it returns, smoke-test the EVAP system from the service port.
- 3Watch where the smoke comes out — that's your leak.
- 4Test purge and vent valves for proper open/close with a scan tool bidirectional command.
Common causes
- Loose, cracked, or wrong gas cap
- Cracked EVAP hose (often near the canister)
- Leaking purge valve
- Leaking vent valve
- Cracked charcoal canister
Typical repair cost
$0 (tighten cap) to $300 (canister or valve).
Related codes
Frequently asked questions
Is it safe to drive?
Yes. It's an emissions code. No drivability impact, but you'll fail inspection.
Working a real vehicle right now?
Let DiagCoach walk you through it live with your specific symptoms, vehicle, and what you've already checked.
Start guided diagnostic →