What Is EVAP System?
The Evaporative Emission Control (EVAP) system seals the fuel system, captures vapor from the fuel tank in a charcoal canister, and routes it into the engine to be burned. It prevents raw fuel vapor from escaping to the atmosphere.
In plain English
Gasoline constantly evaporates, especially in a warm tank. The EVAP system catches that vapor in activated charcoal, holds it, and lets the engine draw it in at the right moment through a purge valve.
The system is sealed and self-testing: the computer pressurizes or pulls vacuum on it and watches whether it holds. When it doesn't, codes like P0442 (small leak) or P0455 (large leak) appear — with a loose gas cap as the most famous cause.
Example
Related trouble codes
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