Powertrain, generic · Auxiliary emission controls

P04EC EVAP System Large Leak Detected - Fuel Tank Side

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

Hybrids with a sealed fuel tank have a valve separating the tank from the charcoal canister and its vent side. CARB allows such sections to be leak-checked separately with their own codes; a Ford patent checks the tank side via tank pressure with the valve closed and the canister side with a leak check module. Conventional systems report the same leak as P0442, P0455 or P0456. P04EC reports a large leak in the tank section: it cannot be brought to test pressure or loses it at once – cap missing or open, line off. Stellantis documents it on the Jeep Wrangler 4xe plug-in hybrid only, whose conventional models report P0455; several bulletins name a cap not closed properly or a trapped tether, with a forced leak test via the scan tool.

Likely causes

Fuel cap not closed properly or tether trapped
Cap or filler neck sealing surface poor
Recirculation or vent line loose at the quick connector
Tank pressure sensor or valve faulty

Symptoms

  • Check engine light on
  • Check fuel cap message, often right after refuelling
  • Possibly fuel smell

Repair estimate

DifficultyEasyDIY possible
Parts and labour€0–250
Time0.1–1 h

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

Parts involved

fuel tankfuel capfuel tank isolation valvefuel tank pressure sensor

Related codes

P04EAP04EDP04EEP0455P0457

References: static.nhtsa.gov, static.nhtsa.gov, static.nhtsa.gov, static.nhtsa.gov.