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

What it means

During the EVAP test, the engine computer has seen a slow pressure change that indicates a very small leak, smaller than the one that sets P0442. The leak does not affect driving, but finding it usually requires a smoke test.

Related codes: P0442P0455P0457P0446P0440

Symptoms4

• Check engine light on.
• Usually no driving symptoms.
• Usually no noticeable fuel smell.
• Failed emissions test.

Possible causes5

• Weak fuel cap seal.
• Vent valve or purge valve not sealing completely.
• Tiny cracks in EVAP hoses or fittings.
• Small leak at the charcoal canister or its connections.
• Leak at the fuel pump module or pressure sensor seal on top of the tank.

How to diagnose5

1. Inspect the fuel cap and try a known-good correct cap.
2. Have a smoke test done with the vent valve commanded closed by a scan tool.
3. Test whether the purge and vent valves seal when closed.
4. Carefully inspect the fittings around the tank and charcoal canister.
5. Use a scan tool to run the EVAP self-test after each repair if the vehicle supports it.

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 vent or purge valve that does not seal fully.
4. Replace the pump module seal or charcoal canister if the leak is there.
5. Clear the codes and drive until the leak self-test completes.

The fix may be a simple fuel cap, but the cost often rises because a smoke test is needed and the vent valve or charcoal canister 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