Cadillac Repair: check engine light, 1991 cadillac seville, cadillac seville

Question
1991 Cadillac Seville, 4 door, 261.000 miles +
Dear Tom Joy,
Though oil pressure and rpm are good, when driving, service engine light comes on and the engine seems fine, so what's causing the service engine soon message to come on?

thanks,
Doug Baker

Answer
Follow this procedure:


1. Ignition ON, Engine OFF.

2. Simultaneously push and hold the OFF and WARMER buttons for 3 seconds and release them.

3. Write down all the LETTERS or NUMBERS that appear in the EXACT order they appear until they stop and let me know what they are

4. turn OFF ignition.