CADILLAC CTS 2003

Question edited for clarity.
Question moved to model category.

By disconnecting the battery, you also disconnected all the set up of the security and engine immobilizer coding.

https://www.google.com/search?q=2003+cadillac+cts+security+system+reset

How do i perform the 2003 Cadillac CTS anti theft reset?

Vehicle History https://www.vehiclehistory.com > questions > how-do-...
To reset the anti-theft system in your 2003 cadillac cts depress the key fob's panic button for five seconds before pressing the lock button twice standing ...
2 answers · Top answer: To reset the alarm on the 2003 Cadillac CTS You have two options. You can pop the hood and disconnect the positive battery cable, then leave it off for ... People also ask
How do I get my Cadillac out of anti-theft mode?"

Look for a button that allows you to slide the physical key out of the fob. Step 2: Turn the vehicle key to unlock the car door without releasing it. Hold the key for 30 seconds in this position. This will signal to your car's system that you have the right key, and will enable you to bypass your car's alarm system.

This link had your same problem last comment may help
https://www.cadillacforums.com/forums/cadillac-cts-first-generation-forum-2003/414449-cadillac-starting-problem-after-serpentine-belt.html
This link had your problem and found a solution
https://www.cadillacforums.com/forums/cadillac-cts-first-generation-forum-2003/890066-car-wont-start-after-replacing-serpentine.html

Assuming the information you provided is correct this http://www.modifiedlife.com/2003-cadillac-cts-car-audio-wiring-chart/ should help you

good luck and thank you
https://www.6ya.com/mr.mike

Fuel filter possible fuel pump dead battery

Try to reset ,how long be off then go for test.

sounds like anti theft device has kicked in needs to be reset dont know how to do that though

Don't do that again! You will need to re-boot the on board computer system by entering a code. Call your nearest Cadillac dealer.

If you need further help, reach me via phone at https://www.6ya.com/expert/lloyd_4256582adacd68ee

Thinking you have a pass lock problem. In the ignition key and tumbler,
all I can do is send you to the dealer ,watch the security light,it's actions will help diagnose the
trouble . My money is on the Ign. switch

car will not come out of park unless the safety switch is activated,,need battery power or jumper cables to do this,,,

Well , it sounds like you need a battery. If a little more info is given on particular vehicle diagnosis would be a lot easier. (ie; year make model).