There is a cat diagnostic test that occurs on 01+ cars when you delete the rear 02. It does not run the test all the time, but you will see your fuel trims fluctuate at times or sometimes a wierd idle. To delete this, you need access to a few more tables that neither dhp or hptuners have. Tiny tuner is about the only program that has the ability to delete these tests out. So you need to have it deleted via tiny tuner or run a emulator. If you want to keep the sensor plugged in but deleted your cat, you need to install it so that it does not see free flowing exhaust or in the exhaust stream. It will throw a cat code if you do not.
