Does the CEL have to light up for there to be codes in the computer? I've got a rough idle from time to time, but no CEL, so far.

I've always thought the CEL needed to come on if there was a stored trouble code.

Thanks in advance

 

No. The light does not have to come on to have codes.

Mook

 

would a place like autozone be able to read them without the CEL?