It
could be the cat, as I did everything else within economic reason to my Nissan 240SX, with over 220K, & it still failed - three times!. As a last resort, I replaced the ORIGINAL cat, & the car became greener'n a Prius.
My '92 SVX with about 130K somehow passed with all original everything, except plugs & PVC valve. Just be sure the car is REALLY warmed up (drive it over 20 miles) before re-taking the test. In my home state of Merryland, if you spend 450 bucks attempting to cure the problem, you get a 2 year reprieval.
I hope Ah-nold is equally forgiving.
Good luck, Ron.