P0442

P0442 is a generic OBD-II diagnostic trouble code that indicates an evaporative emission system leak detected (small leak). It is defined by SAE and used by most modern gasoline-powered vehicles. The EVAP system captures fuel vapors from the fuel tank and routes them into the engine for combustion, rather than letting vapors escape to the atmosphere.

When the EVAP small leak is detected, the ECU stores P0442 and the check engine light turns on. The exact threshold varies by manufacturer, but it typically means a leak that cannot be held under vacuum during testing, such as a loose gas cap or a tiny hose crack.

Common causes include a loose or degraded gas cap and its seal, cracked or disconnected vacuum hoses, a faulty purge valve, a damaged charcoal canister, or a failed vent valve or EVAP solenoid. A recently fueled tank or residual vapor pressure can also trigger the code.

Symptoms are usually a check engine light; drivability impact is often minimal. Some drivers notice a fuel odor or more frequent refueling, but many cases have no noticeable symptoms. Diagnosis starts by confirming the gas cap is present and tight, then inspecting EVAP hoses and connections, followed by a smoke or pressure test to locate leaks.

Repair involves fixing the leak source, clearing the code, and allowing the EVAP monitor to complete. If needed, components such as the gas cap, hoses, purge valve, or canister may be replaced.