Hi, The check engine light on the dash board is turned on I went to AutoZone and the code was P0456.
I changed the Gas Cap but the light is still on. they said it may take a while until the turns off again is that true? do I have to unplug the battery?

 

the ECU checks the system after the 2nd or 3rd drive, it might take a day or so.

 

the ECU does the check of the evap system every 3rd drive, so if the gas cap fixed it, the light will go off on the 3rd drive

 

And fyi that doesn't mean turn the car on drive for 5 mins and repeat. I believe the ECU runs the test once the engine is fully warmed up and has been run for a little bit.

 

The guy at autozone could have removed the code with his scanner. Go back and tell him to clear the code....or you can wait a few days.

 

Not all autozones will clear the codes anymore. At one point they would, then they switched to handing the person the scanner and having them hit the 'ok' to clear the code. Now I have heard some wont clear them for you at all even if you hit the button to do it.