This code only comes on after the car does a test of the EVAP system. The reason the light stays off for a while after you clear the code is because the car doesn’t know there’s a leak. The car will only do the test under certain conditions, for example the gas tank has to have so much gas in it, the outside temperature has to be in a specific range and the car must be driven a certain way. After the conditions are met, then the car does a test and finds a leak and sets the code. On many cars here in Michigan the test doesn’t take place all winter because the temps are too cold. But when spring hits, all them cars that had problems and weren’t tested all winter, suddenly they get tested and check engine lights come on and shops get real busy for a while. You should have it smoke tested to find out where the leak is, then repaired.
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