Cadillac Repair: 96 STS codes, hp gain, gain thanks

Question
I have a 1996 STS and am wondering how to access the diagnostic mode for this car and how to clear the codes.  Also I was wondering what some of the best mods are for these cars for HP gain.
thanks

Answer
1. Ignition key ON. Engine OFF.

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

3. Codes will appaer, If any< with the word HISTORY or CURRENT with each code that displays.

4. After the codes finish displaying, If any, The display will raed PCM?

5. Write down the codes and if they are HISTORY or CURRENT and when you see PCM?, Turn OFF the ignition key.

6. Let me know what the codes are and if they are HISTORY or CURRENT.