Grab your key.
ON-OFF-ON-OFF-ON inside of five seconds (do not crank over to START.)
The CEL/MIL should flash out your codes, and you can then look them up in the Tech Archives on my site.
I.E.: FLASH-FLASH-pause-FLASH-FLASH-FLASH would be DTC 23.
If all you get is DTC 12 (IIRC - check the charts,) that's an "all's well" code.
Note that there are some codes that do not trip the CEL/MIL, and they are indicated on my lists.
(Link in sig.)