Evaporative Emission (EVAP) System Leak Detected (Small Leak)

What it means

During its self-test, the engine computer seals the EVAP system and watches its pressure; if the pressure changes in a way that indicates a small leak, it sets this code. The leak does not affect engine performance, but it lets fuel vapor escape into the air.

Related codes: P0456P0455P0457P0440P0446

Symptoms4

• Check engine light on.
• Occasional light fuel smell, especially in hot weather.
• Usually no driving symptoms.
• Failed emissions test.

Possible causes6

• Damaged or cracked fuel cap seal.
• Small crack in an EVAP hose or fitting.
• Purge valve or vent valve not sealing fully.
• Corroded or cracked fuel filler neck.
• Cracked charcoal canister.
• Leak at the fuel pump module seal on top of the tank (less common).

How to diagnose5

1. Inspect the fuel cap and its seal, and try a known-good correct cap.
2. Have a smoke test done; it is the most accurate way to find small leaks.
3. Inspect hoses and fittings near the tank and charcoal canister.
4. Test whether the purge and vent valves seal when closed.
5. Inspect the filler neck for rust or cracks.

How to fix5

1. Replace the fuel cap with one that meets the vehicle specification.
2. Replace the hose or fitting where smoke escapes.
3. Replace a purge or vent valve that does not seal.
4. Replace the filler neck or charcoal canister if cracked.
5. Clear the codes and drive until the leak self-test completes.

The fix is often a simple fuel cap; the cost rises when a smoke test is needed and the vent valve or filler neck must be replaced.

Prices are rough estimates for common cars at independent workshops and vary with the car and the source of the part.
Prices last updated: September 2026

Frequently asked questions