2005 cts @ 100,000 what service needs to be done?

The owners manual says that normal driving conditions the belt change is at 100,000 miles. Severe service schedule is every 50,000 miles.
https://my.gm.com/content/dam/gmownercenter/gmna/dynamic/manuals/2005/saturn/vue/2005_saturn_vue_owners.pdf

Your mechanic caused this. Take it back and have them fix it.
Major work like this done at a dealer will also get you a 12 month - 12,000 mile warranty.

Google the codes & see what they refer to

Most likely the two Upstream Sensors failed,
you can replace at 100,000 miles on all vehicles,
even if you got no codes, the switching times will
be too slow by then

How to change a fuel filter on a 2003 Cadillac CTS - YouTube

? 11:01
https://www.youtube.com/watch?v=SRI7SPzVzvk
Jun 2, 2014 - Uploaded by 2LateIWon
How to change a fuel filter on a 2003 Cadillac CTS. ... Lately... my 2007 cadillac CTS (just hit 100,000 miles) tends to shake for may a second if ...

If it has never been changed, I would recommend you get it done now, if you take it to a service shop, nothing has to be removed, the oil changer plugs right into the transmission lines. on the 3rd year, I recommend the ****** filter changed along with fluid.

Your best longevity check is to set up and maintain a consistent oil and filter replacement schedule...Depending on your planned driving habits...your owners manual should recommend you change these every 5000-7500 miles or every 3 months whichever occurs first. Oil products have inproved for many years. The synthetic oil blends are the best for performance and mileage...most exceed your Cadillac specs...Mobil 1, and Castrol full synthetic are by preferences...No special tune-up or other maintenance should be needed at this time...watch for serpentine belt...100,000 miles...plugs and plug wires...100,000 miles...suspension parts vary between 75K to 100K before replacement...Hope this helps.

Best bet is to consult your owners' manual, however, there is one thing to expect to come up soon that won't be mentioned there. Delco alternators usually croak at about 62-65,000 miles like clockwork. Be prepared for it.

valued by its mileage
wires for the spark plugs @ 50,000 miles.
spark plugs @ 100,000 miles
pcv @60,000 miles
air filter when needed or 12 months
fuel filter @25,000 miles

http://www.cadillacfaq.com/faq/answers/pdf/2k05cts_ctsv.pdf < try this link should fix you up let me know please..gl...dc

no not at all, keep what you are doing your doing something right to have a car last that long!!!