Powertrain, generic · Auxiliary emission controls

P0442 EVAP System Leak Detected (small leak)

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

The evaporative emission (EVAP) system stores fuel vapour from the tank in a charcoal canister; a purge valve lets the engine draw it off, and a vent valve opens the canister to fresh air. P0442 reports a small leak; what size that means depends on the maker. Ford detects 0.040 in (1 mm) with the engine running: the vent valve closes, engine vacuum pulls the tank down, the purge valve closes and a pressure rise above 2.5 inH2O in 15 s sets the code (0.020 in is P0456). GM uses the natural pressure change after switch-off for 0.020 in and averages several tests. Pump systems at VW and Audi compare against a reference leak. A worn or loose fuel cap is the most common cause.

Likely causes

Fuel cap seal worn, wrong or not clicked in
Cracked or porous EVAP hoses or leaking connections
Purge or vent valve does not seal
Leak detection pump itself leaking (VW/Audi)
Filler neck corroded, tank or sender seal leaking

Symptoms

  • Check engine light on
  • Possibly slight fuel smell
  • Readiness or emission inspection not passed
  • No change in driving

Repair estimate

DifficultyMediumDIY possible
Parts and labour€15–400
Time0.2–3 h

Typical range across vehicles; the real cost depends on what the testing finds.

What to check first

  1. Replace a worn fuel cap
  2. Smoke-test the system
  3. Inspect hoses near the tank

Parts involved

evap systemfuel capevap hosesfuel tank pressure sensor

Related codes

P0455P0456P0457P0441P043EP0496

References: fordservicecontent.com, newtonnet.co.uk, gsi.ext.gm.com, saabwisonline.com.