Powertrain, generic · Auxiliary emission controls

P0456 EVAP System Leak Detected (very 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. P0456 reports a very small leak of 0.020 in (0.5 mm), as CARB requires. Ford uses the engine-off natural vacuum test: after switch-off the closed system must build at least about 190 Pa pressure or 125 Pa vacuum, judged statistically. Saab's Bosch ME9 also tests with the engine off for up to 45 minutes; VW and Audi use a leak detection pump. GM reports this leak size as P0442 instead. The code often appears only after many trips and depends on the weather.

Likely causes

Fuel cap seal worn or cap not clicked in
Purge or vent valve not sealing
Porous hoses or O-rings, hairline crack in canister or filler neck
Leak detection pump itself leaking (VW/Audi)

Symptoms

  • Check engine light on (possibly a check fuel cap message)
  • Possibly fuel smell
  • EVAP readiness or emission inspection not passed

Repair estimate

DifficultyMediumDIY possible
Parts and labour€15–450
Time0.2–3 h

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

What to check first

  1. Replace the fuel cap if worn
  2. Smoke-test the system

Parts involved

evap systemfuel capevap hosesevap leak detection pump

Related codes

P0442P0455P0457P0441P0446P043E

References: fordservicecontent.com, saabwisonline.com, static.nhtsa.gov, static.nhtsa.gov.