My check engine light was on all last week. I made an appointment to take the thing in and have it checked. Last night it went off. That makes no sense.

I thought even intermittent problems would have to be reset.

 

The code should still be in there. Take it to the dealer to find out why it came on.

 

The light merely tells you a code was thrown. If the condition that caused the code is not present after so many ignition cycles, the light will go off (there are certain more serious problems that will not allow the CEL to go away). The H3 stores any code thrown for 300 ignition cycles. An ignition cycle begins at start up and ends when the vehicle is shut off, only after it reaches full operating temperature.

Or, yeah..... what YellowFin said.

 

more than likey your gas cap was not tight. this evap code will reset after a few ignition cycles

 

go to an oil change place or even an auto zone its free there, if its a open gas cap code thrown at the dealer your payin imo