Cadillac Repair: 96 seville Battery no charge, number combinations, code displays

Question
Just replaced the alternator that was bad. Now when I start the car the monitoring system will read 13.5 volts for about 40 seconds and return to no charge. Also if the rpm's go below 500 it will read amperage but will retun to no charge when the rpm increase. The alternator is testing fine @ 18.8 and it is testing fine at the battery.(new bttery).
Do you have any advise.
Thank you,
Jim

Answer
You either have a wiring problem, A fault in the cluster display or a fault in the Body Control Module (BCM) computer.

You need to retrieve the codes from the computer via:

1. Ignition 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. On your fuel data display you will see LETTER and NUMBER combinations appaer along with the word CURRENT (C) or HISTORY (H) as EACH CODE displays.

4. The display will stop when you see PCM?

5. Write down EXACTLY what displays on the fuel data display as if you were video taping it and let me know what it displays.

6. turn ignition OFF.