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Is your check-engine light showing P0442 or P0456? On a MINI Cooper or BMW, the most common cause is a worn gas cap seal. Heat and fuel fumes harden the rubber until vapor slips past.

The gas cap fuel seal for BMW/MINI (16116756772 / 16117222391) is the cheapest first move. It costs $10-30. A shop smoke test costs $90-150 and often finds nothing the cap had not already explained.

What the EVAP system is, in plain words

EVAP is short for evaporative emissions system. It is a sealed loop that keeps gasoline vapor inside your tank instead of the air. The fuel cap is the only lid on that loop.

Your car checks the loop by pulling the tank into a slight vacuum. If the vacuum fades too fast, the computer stores a leak code. A hard, cracked cap gasket is the leak it finds most often.

What the three codes mean

All three codes point at the same sealed loop. They differ only in how big a leak the computer measured:

• P0440 — general EVAP fault. The system saw a sealing or purge problem without grading the size. A loose or worn cap is a first-line suspect.
• P0442 — small leak. This means a leak about the size of a 0.040-inch hole. It is the classic worn-gasket code.
• P0456 — very small leak. A marginal cap seal can sit here, but so can a cracked hose or a stuck valve.

None of these codes means liquid gasoline is leaking. They only detect vapor escaping, which is why the car drives normally with the light on. Your state emissions inspection will still fail it.

One cap, two numbers, dozens of cars

16116756772 and 16117222391 are the same tethered cap. Some catalogs list a third reference, 16116754491. Order by your car, not by which number looks familiar.

Check the number molded into your old cap, or look your car up by VIN. A cap that threads down but seats wrong keeps the code alive. That is the most confusing failure this system produces.

The same OE-number habit protects the rest of the emissions chain. It applies to the upstream + downstream O2 sensor pair for the 2002-2008 MINI Cooper 1.6L and the EPA-compliant direct-fit catalytic converter for the 2007-2015 Cooper 1.6L.

The cheapest-first check order

Work through these five steps in order. Most cars are done by step 3:

1. Pull the cap and look. Check the gasket for cracks, flat spots and fuel swelling. Check the filler neck rim for damage too.
2. Reseat and tighten until it clicks. On the bayonet style, thread it firmly home.
3. Not sure? Replace it anyway. At $10-30 the cap costs less than one hour of diagnostic labor.
4. Clear the code and drive. The monitor needs several days of mixed driving to re-run. Code gone and staying gone means you are done.
5. Smoke test only if the code returns. The machine fills the loop with visible smoke, and the escaping plume marks the leak.

If the code comes back

A new cap removes the cheapest suspect. If the code still returns after several drive cycles, the leak is inside the loop:

• The purge solenoid — the valve that lets stored vapor into the engine. Stuck open or stuck closed, it sets these codes.
• Brittle underbody vapor hoses, which crack at the clamps first on 20-year-old cars.
• The vent valve or the charcoal canister area.

KOEEP covers the GM side of that same repair: the purge valve replacement for Chevy Avalanche/Camaro (214-1680 equivalent), the 12597567 purge solenoid for Chevy/Buick/GMC and the 12582167 solenoid variant. MINI and BMW use the same valve concept under their own numbers, on or near the intake manifold.

Different badges, identical EVAP physics. The failure modes are written up in the purge solenoid 12597567 guide for Chevy/Buick/GMC and the 12597341 purge valve guide for Isuzu/Saab/Pontiac/Saturn.

Caps, valves, hoses and everything else in the fuel path live in the air and fuel delivery collection.

Frequently asked questions