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DTC codes / P04xx · Auxiliary emission controls / P04EE

P04EEEVAP System Very Small Leak Detected - Fuel Tank Side

P04EE indicates that the engine computer has detected a very small evaporative emission (EVAP) system leak, specifically on the fuel tank side of the system. The computer performs a pressure or vacuum decay test and observes a leak rate that is smaller than a large leak but still exceeds the threshold for a very small leak, which is typically equivalent to a pinhole-sized opening.

SystemPowertrain
Code typeGeneric (all makes)
SeverityLow
Fix difficultyIntermediate
AreaAuxiliary emission controls

Symptoms you may notice

  • Illumination of the malfunction indicator lamp (MIL) on the dashboard, often with no other noticeable symptoms.
  • A faint fuel odor may be present around the rear of the vehicle or near the fuel tank area.
  • In some cases, a slight hiss or whistle may be heard when the fuel cap is removed, indicating a pressure or vacuum issue.
  • The driver may notice no drivability problems, as this code does not typically affect engine performance.
  • On some vehicles, a message may appear in the driver information center indicating a check fuel cap or EVAP system issue.

Common causes, most likely first

  1. A loose, damaged, or missing fuel filler cap is the most common cause of very small EVAP leaks.
  2. A small crack or pinhole in an EVAP hose or line on the fuel tank side, often due to age or abrasion.
  3. A faulty or sticking EVAP canister purge valve that does not seal properly, allowing a small leak.
  4. A leaking fuel tank pressure sensor or its seal, which can allow a very small amount of vapor to escape.
  5. A small leak from the fuel tank itself, such as a seam or gasket leak, though this is less common.
  6. A malfunctioning EVAP canister vent valve that does not close completely, causing a small leak during testing.
  7. A leak at the fuel pump module seal or gasket where it mounts to the fuel tank.

How to diagnose and fix it

  1. Inspect the fuel filler cap for proper tightness, cracks, or a damaged seal, and replace it if any issue is found.
  2. Perform a visual inspection of all EVAP hoses and lines on the fuel tank side for cracks, abrasions, or loose connections.
  3. Use a smoke machine to introduce smoke into the EVAP system and locate the source of the very small leak.
  4. Check the operation of the EVAP canister purge valve and vent valve using a scan tool to command them open and closed, and verify they hold pressure or vacuum.
  5. Test the fuel tank pressure sensor for proper operation and check its seal for leaks.
  6. If no external leak is found, perform a pressure decay test on the fuel tank itself to check for internal leaks or a faulty tank seal.
  7. Replace any faulty components such as hoses, valves, or the fuel cap as needed, and clear the code to verify the repair.

Small Leaks Often Hide in Plain Sight

  • A very small EVAP leak can be caused by a fuel cap that is not tightened to the click, so always check the cap first before replacing any parts.
  • The EVAP system may only run its leak test under specific conditions such as a cold engine and a certain fuel level, so the code may not set immediately after a repair.
  • A leak on the fuel tank side can sometimes be caused by a faulty fuel tank pressure sensor that is not sealing properly, which is often overlooked.
  • Smoke testing is the most effective way to find very small leaks, but the smoke may escape from a location that is difficult to see, such as the top of the fuel tank.
  • This code does not affect engine performance or fuel economy significantly, so it is safe to drive with it, but the leak should be repaired to prevent fuel vapor release.

Can I keep driving with P04EE?

It is generally safe to continue driving with this code, as it does not affect engine operation or safety. However, you should avoid topping off the fuel tank and have the leak repaired promptly to prevent fuel vapor from escaping into the atmosphere.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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