An EVAP leak is a fault in the evaporative emission control system (EVAP) that captures and stores fuel vapors from the cars fuel tank and burns them off in the combustion chamber when the engine is running. An EVAP leak occurs when these vapors escape from any part of the system, which can cause a fuel odor or a check engine light to appear. The most common causes of EVAP leaks include bad seals and O-rings, a failing purge valve, a damaged hose or vent, or a defective leak detection pump. Loose or damaged fuel caps can also cause significant EVAP leaks. While it is safe to drive with an EVAP leak, it is important to identify and repair it as soon as possible, as it can lead to serious problems and uncontrolled emissions that pollute the air. To diagnose an EVAP leak, you can check for a check engine light or use an OBD-II scanner to check for specific error codes related to the EVAP system. It is best to have a professional mechanic inspect and repair the EVAP system, as it is a complex system.