P0442EVAP system small leak detected

Means the EVAP monitor built vacuum (or pressure) but could not hold it—the leak is in the small-orifice bucket, often framed around a ~0.040 in path rather than a missing hose. That is why this code is harder than P0455: the system almost seals, then bleeds down just enough to fail the timer. Drivers typically get a check-engine light with no stumble and a stubborn EVAP readiness flag that keeps failing state/provincial inspection. Freeze frame is usually a quiet cruise or hot-soak window; there is rarely a fuel-trim complaint because this is vapour containment, not Bank 1 metering.

Probability still starts at the filler. A gas cap that clicks but has a hardened, nicked, or contaminated seal is the classic small-leak source—tight enough to pass a casual glance, loose enough to fail the monitor overnight. Next come weep paths: purge valve that does not fully seat, vent solenoid that leaks when commanded closed, cracked plastic EVAP lines that only open when hot, canister seams, and filler-neck O-rings. FTP sensor drift can exaggerate a tiny leak into a fail, but prove sensor sweep before you chase ghosts. Do not treat P0442 like P0455: you will not usually find a hose flopping open on the frame rail.

Diagnosis is patience plus low-pressure smoke. Confirm the correct cap and seal first, then run the OEM EVAP seal / vacuum-decay test while graphing FTP. Watch how fast vacuum decays after purge and vent are commanded closed—a steep drop is still “large”; a slow bleed is the P0442 signature. Smoke at the OEM-specified low pressure only, with the system sealed and the shop bright enough to see a wisp at the cap, purge valve body, vent filter, canister, and every plastic tee. Lightly flex lines and the filler neck while smoking—heat-cycle cracks show up as intermittent smoke. Ultrasonic or soapy water at fittings helps when smoke is faint. Command-test purge and vent for internal bypass: a valve that holds against hand vacuum on the bench but weeps on the car still fails the monitor.

Replace the cap or the weeping valve/line when smoke or decay timing names it. Dig elsewhere when smoke is clean yet decay still fails (FTP calibration or ECM monitor enable), when the code only sets after refueling (filler-neck seal), or when a related P0455 was “fixed” with a cap but a micro-leak remains. Recheck after the repair on a full hot-soak EVAP enable—many micro-leaks only fail once the plastic lines and canister have heat-cycled, so a cold bay pass is not proof. System context: small-leak EVAP is the strict neighbour of large-leak P0455 and general EVAP P0440—same canister and valves, tighter pass/fail. Fix the weep before you burn days on readiness drive cycles.