Cadillac Repair: SERVICE ENGIN SOON LIGHT, port fuel injection, low altitude

Question
THE SERVICE ENGINE SOON LIGHT IS COMING ON MORE FREQUENTLY.
USUALLY IN THE HILLS OR MOUNTAINS BUT NOW IT'S COMING ON AT LOW ALTITUDE.
1991 SANDAN DEVILLE 4.9L PORT FUEL INJECTION V8.
THE LIGHT DOES NOT COME ON RIGHT AWAY ON STARTING. AND SOMETIMES DOES NOT COME ON WHILE DRIVING FOR HOURS.
BUT IT IS COMING ON WAY MORE FREQUENT.
WILL THIS CAUSE ME TO FAIL CA SMOG ?
WHAT ARE THE POSSIBLE CAUSES ?


Answer
1. Turn ignition switch ON. Engine OFF.

2. Simultaneously push and hold the OFF and WARMER buttons on the climate control panel for 3 seconds and release the buttons and write down every thing that appears on the screen until it stops displaying. Write down EVERYTHING you see in the EXACT order in which it displays as if you were video taping the display.