P04EE: EVAP System Very Small 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. P04EE reports a very small leak (0.020 in) in the tank section, usually checked with the engine off. Stellantis documents it on the Jeep Wrangler 4xe – cap, tether or filler tube, with a scan-tool leak test before replacing parts – and Ford on the C-Max, Fusion and MKZ hybrids and Energi of 2013–17, together with P0456 and P0457, fixed by a tighter purge valve and software.

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
No change in driving

Most likely causes

Fuel cap seal deformed or dirty, tether trapped
Purge valve not sealing (Ford hybrids) – plus software
Leaking quick connector or vent line at the tank
Hairline crack in tank lines or flange seal

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 P04EE means

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

Frequently asked questions

Can I keep driving with code P04EE?

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 P04EE?

The most common causes are: fuel cap seal deformed or dirty, tether trapped; purge valve not sealing (Ford hybrids) – plus software; leaking quick connector or vent line at the tank.

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.

P04EE: EVAP System Very Small Leak Detected - Fuel Tank Side