P04EC: EVAP System Large Leak Detected

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.

Low severity. Can I keep driving?Yes, you can normally keep driving. If there is a strong smell of gasoline, find the leak before continuing and do not smoke nearby.

Symptoms

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

Most 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

What to check, in order

Start with the simplest. You can tick off each step.

Start with the fuel cap: tighten it fully and check its seal
Inspect the hoses and connections around the tank and the charcoal canister
Use the scanner to test the purge and vent solenoid valves
Run a smoke test to find small leaks

Good to know

Repair difficulty: easy
It affects emissions.

What each character of P04EC means

P: Powertrain: engine and transmission
0: Generic code: same on every make
4: Emissions
EC: Specific fault in that system

Frequently asked questions

Can I keep driving with code P04EC?

Yes, you can normally keep driving. If there is a strong smell of gasoline, find the leak before continuing and do not smoke nearby.

What causes code P04EC?

The most common causes are: fuel cap not closed properly or tether trapped; cap or filler neck sealing surface poor; recirculation or vent line loose at the quick connector.

Related codes

Sources

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.

P04EC: EVAP System Large Leak Detected - Fuel Tank Side