P04EE: Evaporative Emission System Very Small Leak Detected — Fuel Tank Side
What to do
Check the filler cap seal even though the leak is described as very small. A rubber seal that has hardened with age leaks exactly this much, and it is by far the cheapest thing to rule out. Refit the cap until it clicks and give it a few days.
Ask for a smoke test rather than a visual inspection. The hole here is around half a millimetre — too small to find by looking — and asking for the right test by name avoids paying for hours of searching.
Mention if the fault appears mainly in cold weather. Seals shrink as they cool, so a leak that only opens when cold can pass a warm workshop test perfectly, and knowing that changes how the garage tests it.
The car drives normally. This matters for the MOT, so allow time before the test rather than booking it the same week.
What this code means
A very small fuel vapour leak has been found on the fuel tank side of the system.
Very small is the tightest threshold the system can test, and it is the hardest code in this family to chase. Where a large leak is typically a cap left off, a very small leak is a hole of around half a millimetre — smaller than a pinhead, invisible, and often not leaking at all when the system is at rest.
That difficulty shapes the whole approach.
- A smoke test is close to essential. Looking for a hole this size by eye is not a realistic method, and asking for one directly avoids paying for hours of inspection that will not find it.
- Temperature matters. These tests run under specific conditions, and a leak that only opens when a seal has cooled and shrunk can pass a warm workshop test perfectly.
- The seals are the usual culprits rather than the hard parts: the filler cap seal, the fuel sender O-ring on top of the tank, the filler neck seal, and hose unions that have hardened with age.
Do not skip the cap just because the leak is small. A seal that has hardened rather than failed leaks exactly this much, and it remains the cheapest thing to eliminate.
Spiders and insects are a genuine, documented cause — a web or nest in a vent line changes how the system breathes and can present as a small leak. It is not a joke finding; it is a common one.
Likely causes
Start here
- Perished fuel cap seal · easy
- Perished fuel filler or sender seal · moderate
- Cracked or perished EVAP hose · moderate
Less common
- Leaking filler neck seal · moderate
- Leak in the evaporative system · moderate
Symptoms
Components involved
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
Be the first to write this up
Nothing posted about this yet. Whatever you found is worth writing down — even a dead end saves someone the same afternoon.
What makes one worth reading:
- The car — make, model, year and engine. The same fault behaves differently on each.
- What you measured, not only what you replaced.
- What actually fixed it — or that nothing did, which is worth knowing too.
Sign in or create an account to add what you found about P04EE.