Cadillac Repair: Key stuck in ignigtion, d rive, common denominator

Question
QUESTION: Hello. I was browsing the web trying to find an answer and luckily came across this site. Here's my problem. I have a 2003 Cadillac CTS. Driving home from work yesterday, I noticed my anti-theft light was on, along with my traction control light. (weird). I came home, and was unable to get my key out of the ignition. Also, my car wouldn't start back up; just a clicking noise. Because the ignition wouldn't turn fully off, of course, overnight it drained my battery. Today, I replaced the battery with a brand new one. My car is able to start up (GREAT), but still the key wont come out. Also, I'm unable to move my gear shift knob (automatic) out of park. To avoid draining the new battery, this time I unplugged the red cable. ANY advice would be greatly appreciated, as I'm trying to avoid having my towed to the shop because I just spent $900 on valve cover gaskets, and still need new brakes and tires within the next couple of weeks.

ANSWER: John,
Verify that the shifter linkage is okay. Sounds like it's not getting into PARK totally. If it is, then check the ign. lock cylinder.

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QUESTION: That's just it. The Light that verifies whether you're in (P)ark, (D)rive, (N)eutral, etc doesn't come on. Like when I first noticed the my anti-theft light was on, I looked down at my geart shift and the light next to the D (even though I was driving) wasn't on. Same with now, I changed the battery, it starts up, but still can't move the gear shift knob. And the (P)ark light isnt on. So that tells me that something isn't reading/registering correctly. But even though I Push/Pull the knob as much as I can, it isn't moving. Didn't want to break it. (although out of fustration, I'm sure I could have). I've asked another tech, and he also mentioned the Ignition Lock Cylinder. ...So that seems to be the common denominator.

Answer
John,
There's also a brake interlock feature that must be activated in order to move the shifter. With key-on, do you hear the brake/shifter interlock clicking when you press the barke pedal?
Also, looking at the system schematics, it's going to take a little scan-tool investigation to see what module is getting what signal (or not). You have the range switch at the trans telling the TCM (Transmission Control Module) what gear it's in but the Park/Neutral signal bypasses the TCM and is sent directly to the ECM. My guess is the ECM then processes the signal and controls the gear display and then the shift interlock is what physically allows the shifter to move. But, I keep going back to the ignition lock cylinder as a point of failure. That's still probably where I'd start. I can't see anything that should stop the key from being able to be turned all the way off but traditionally speaking, there is a mechanical interlock that stops the key from being pulled unless the shifter is in park.