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P0442 Evaporative Emission System Leak Detected (Small Leak)

A small leak in the fuel vapour system — harder to find than a gross leak because you usually can't see or hear it.

Emissions

Same test as P0455, but the leak is small — the system held pressure, just not well enough. Roughly a pinhole. Because a small leak is invisible and silent, this is one of the codes where a smoke test stops being optional and becomes the efficient way to do the job.

Diagnose P0442 on your specific vehicle Add your year, make and model for ranked causes, repair videos and the exact parts you need

Can I keep driving?

Driveable

Yes, with no effect on how the car drives.

How serious

Low. Emissions failure and a small amount of vapour escaping; nothing mechanical at risk.

Symptoms you'll notice

What causes P0442

Ordered by what to check first — how likely each cause is, weighed against what it costs to rule out. Working down the list in order is what stops you replacing an expensive part to fix a cheap problem.

01

Aging gas cap seal

Still worth checking first even for a small leak — a hardened seal leaks slowly rather than grossly, which fits this code exactly.

02

Pinhole crack in an EVAP hose

Age-hardened rubber cracks in small ways first. These are genuinely difficult to spot by eye, and often only leak when flexed or warm.

03

Leaking purge or vent valve seat

A valve that seals almost, but not quite, produces a small leak rather than a gross one.

04

Cracked charcoal canister or fuel tank seam

Small cracks from age, corrosion or impact damage under the car.

05

Leaking fuel tank sending unit gasket

The seal around the fuel pump and sender assembly on top of the tank hardens with age. Commonly the answer when everything visible checks out, and it requires dropping the tank or accessing it through the floor.

How to diagnose it

  1. Inspect and replace the gas cap if the seal is at all hardened or cracked — it's the cheapest possible outcome.
  2. Smoke test the EVAP system. For a small leak this is the practical approach; hunting by eye wastes hours.
  3. Flex EVAP hoses by hand while inspecting, since small cracks open under movement.
  4. Check the purge and vent valves for proper sealing.
  5. If nothing else shows, inspect the fuel tank sending unit gasket.

Parts you might need

Tools for the job

Related trouble codes

Get the parts list for your vehicle Ranked causes, tutorials and live part prices for your exact year, make and model

Fitment matters. Causes and parts above are the common cases for P0442 across vehicles. The specific part numbers, procedures and torque specs vary by year, make, model and engine — always confirm against service data for your vehicle before buying parts or starting work.