Just posting this info for other that don't know, hope it helps.
Hey just changed the fuel filter and did an oil change + filter on my 04' CTS sport. First maintenance since I bought it. Changing the oil on this CTS is very easy, especially with the oil filter on top. The fuel filter was a bit hard not much room to work around.
But not hard to do, with the right tools. You definitely have to get the quick disconnect for the fuel lines, you'll need the small ones 5/16 in. and 3/8 in. disconnects. Remember to open the fuel cap to get the pressure of the lines.
Also the fuel line going in to fuel filter is a 5/8 in. and you'll need a small adjustable wrench or maybe a 20 mm. which I didn't have for the filter. Make sure you spray WD-40 before you start on the outside of the fuel line nut, which I'm sure is very rusty. Works wonders to make it easier to break the nut of the fuel filter.
The fuel filter was the original replaced at 100203 miles. Also when buying the new fuel filter try and get one with the outside cartridge that is smooth or same size from top to bottom. I make's it a lot easier to reinstall thru the plastic holder.
The one I bought had a large lip on the top next to nut (out put) side to engine, which needs to be installed from the double lines first. Which makes you remove the plastic holder off completely, with the other lines above it as well. Which is not easy to do.
I've had to remove these line before and are very hard to remove from these U-clips. I'm sure there is a special tool for these lines which I don't have. But the plastic holder had enough space just to push the new fuel filter thru and reinstall it.
Just happy I did not brake the fuel line a little rusty on the outside of the nut.
Also forgot to said that the you'll need 13mm wrench for the oil pan screw and a 24mm for the oil filter cartridge.
Other then that very easy to work on. My next work is going to be the spark plugs.
Well like I said this is just info, for those that may need some assistance.
Good maintenance makes your car go a long way. My last car was an 03' Montercarlo SS with 329,580 miles that's what good maintenance does.
Hope I can get the same from my CTS.