My codes do not read when hooked to the computer.
I own a 1994 DeVille and you do not hook it up to the mechanics diagnostic computer, IT HAS IT'S OWN ON-BOARD DIAGNOSTICS that are accessed through buttons being pushed on the climate control panel. I know how mine works but not your's. I would guess if this was on 1994 it's probably on 2004, Try www.cadillacforum.com for info - they have stuff broken down my model and year under all kinds of sub groups. Also there is a youtube demo on on-board for the 1994 deville so maybe one there for you too.
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