P0442 – Evaporative Emission Control System leak Detected (small leak)
What does P0442 mean?
The EVAP system has detected a small leak — the same system as P0455, but the leak is smaller and therefore harder to locate. The computer detected that the sealed fuel vapor system lost pressure or vacuum slowly during its self-test.
What causes P0442?
Listed from most to least common:
- 1Fuel cap not fully tightened or with a worn seal
- 2Small crack in an EVAP hose
- 3Slightly leaking purge or vent valve
- 4Pinhole leak in the charcoal canister
- 5Degraded O-ring or seal at an EVAP connection
Code breakdown
Common symptoms
- Check engine light on
- Normal drivability
- Failed emissions test
How to diagnose
- 1Tighten or replace the fuel cap and clear the code first — it is the cheapest possible fix.
- 2Smoke-test the EVAP system. For small leaks this is effectively mandatory, since visual inspection rarely finds them.
- 3Pay close attention to hose connections, grommets, and the canister body during the smoke test.
- 4Test purge and vent valve sealing.
No drivability impact, but the vehicle will fail emissions testing. Small leaks can be tedious to find.
Common fixes and estimated costs
| Repair | Estimated cost |
|---|---|
| Replace fuel cap | $15–$60 |
| Replace cracked EVAP hose or seal | $50–$250 |
| Replace purge or vent valve | $100–$350 |
| Replace charcoal canister | $250–$700 |
Costs are rough US estimates including parts and labor. Actual pricing varies significantly by vehicle, region, and shop rates.
Good to know
P0442 is one of the more frustrating codes to chase without a smoke machine. If a new fuel cap does not fix it, a shop smoke test is usually cheaper than replacing parts by guesswork.
Related codes
This information is provided for general reference only and may vary by manufacturer, model, and year. It is not a substitute for professional diagnosis or repair.