What is evaporative leak in a car?

Answer 1

On modern cars the fuel tank, hoses, etc... are sealed to prevent gas fumes from venting in to the air we breathe. Because fuel vapors can cause horrible air quality the EPA requires all vehicles sold in the US to have a functioning system to manage these sealed vapors. Part of this system is a set of components that detect if there is a leak from the fuel tank in to the atmosphere. The computer only tests for leaks when the conditions are just right so sometimes it takes several weeks after a leak has formed for the computer to detect the problem and trigger a 'check engine light'.

Tracking down evap leaks can be very difficult because the system has an array of hoses, sensors, canisters, and valves. Diagnosis can require expensive test equipment such as automotive leak detection smoke generators.

The most common leak is the fuel cap. I would replace the fuel cap because it is cheap. Have someone with a scan tool clear the trouble code from the computer. Drive the vehicle for several weeks to see if the problem reoccurs. If problem persists you will need to have it diagnosed by a reputable repair technician.