Cadillac Repair: diagnostics, control panel buttons, code displays

Question
QUESTION: I have a 1990 Sedan DeVille. Check engine light is on, and engine running rough..using too much gas. I stopped at Autozone to have light checked, but they said car was too old for their equipment. They gave me a small metal key with 2 prongs sticking out of end. They said I should put it in somewhere under the dash, and turn ign. key on, and I could get the codes somehow. I did find a "diagnostics terminal" or something marked diagnostics under the dash, but it appears to have about 8 or 10 holes, and no obvious place to put the 2 prong key.  Any suggestions?  Thanks !

ANSWER: You can get the CODE or CODES by using the CLIMATE CONTROL PANEL buttons.

1. Turn the ignition switch to the ON position ONLY. Do NOT start the engine.

2. Simultaneously push and hold the OFF and WARMER(^) Buttons on your climate control panel for
  3 seconds and release them.

3. Immediately look at your fuel data display panel and you will see the CODE or CODES
  displaying followed by the word History or Current AFTER EACH CODE displays.

4. Write down EVERYTHING that you see on the fuel data display panel or better yet, Video tape
  the display until it stops displaying codes and e-mail the video or the written codes to:
  onlineautohelp@msn.com

5. Turn ignition key OFF.


---------- FOLLOW-UP ----------

QUESTION: Found the codes with the info. above. Didn't get exactly what I anticipated. Here goes: 8.8.8 / .  .E / E30 /  E39 /  E49 /  E52 /  E55 /  E62 /  E97 /  E98 /  .E.E /  E49 /  E55 /  E62 /  . 7.0  ----/ It just stays lit on . 7.0 and doesn't go any farther...never a word : history, current, or any other word.  Thanks again.

Answer
OK what you need to do now is to CLEAR (erase) ALL the codes and see which ones come back as E codes and or EE codes.

To CLEAR the codes:

1. Redo the same thing as you did to get these codes and when the display stops and you see .7.0.

2. Simultaneously push and hold the OFF and Hi (^) buttons until you see E.0.0 and then release the buttons.

3. Turn ignition key OFF for 2 minutes and then recheck for codes and let me know which codes reappear as E and or EE codes.