Summary
P0442 means the PCM found a small leak in the EVAP system — the sealed vapor recovery system connected to your fuel tank. The most common cause is a worn gas cap seal (40%), followed by small cracks in EVAP hoses (25%) and a failing purge or vent valve (20%). Unlike P0455 (large leak), P0442 small leaks are harder to find visually and often require a smoke test to pinpoint. Start by replacing the gas cap ($5–$15).
Severity: Low — emissions only, no drivability impact
Safe to drive: Yes — no effect on engine performance
Repair cost: $5–$300 depending on cause
DIY difficulty: Easy (gas cap) to Shop-recommended (smoke test)
What does P0442 mean?
The EVAP system seals fuel vapors inside a closed circuit: fuel tank → hoses → charcoal canister → purge valve → intake manifold. The PCM tests this system for leaks by applying a slight vacuum or pressure and monitoring decay. P0442 means the system lost pressure at a rate consistent with a small leak — larger than a pinhole but smaller than what triggers P0455 (large leak).
Small EVAP leaks are notoriously difficult to find because they can be caused by a hairline crack in a hose, a slightly deteriorated O-ring, or a microscopic gap in a connection. Visual inspection often misses them. A professional smoke test is the most reliable diagnostic method.
This code has no effect on engine performance. The EVAP system is completely separate from the engine's combustion air-fuel management.