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

What it means

During its self-test, the engine computer tries to pull vacuum in the EVAP system; if vacuum never builds or builds very slowly, it sets this code. It means there is a large opening in the system, most often a missing or loose fuel cap.

Related codes: P0457P0442P0456P0446P0441

Symptoms4

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

Possible causes5

• Fuel cap missing, loose or the wrong type.
• EVAP hose disconnected or badly cracked.
• Purge valve not opening, so no vacuum is drawn during the test.
• Vent valve stuck open.
• Cracked charcoal canister or fuel filler neck.

How to diagnose5

1. Check the fuel cap first, making sure it is present and tightened until it clicks.
2. Inspect visible hoses and the charcoal canister for disconnections or cracks.
3. Command the purge and vent valves with a scan tool and confirm they open and close.
4. Have a smoke test done to find the opening precisely.
5. Watch the tank pressure sensor during the test to confirm vacuum builds.

How to fix5

1. Tighten the fuel cap or replace it with a correct one.
2. Reconnect a loose hose or replace a cracked one.
3. Replace a faulty purge or vent valve.
4. Replace the charcoal canister or filler neck if cracked.
5. Clear the codes and drive until the leak self-test completes.

The fix is often the fuel cap or a disconnected hose at low cost; the cost rises when a 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