I had the engine light come on and took it to a dealer in Vancouver, Canada. They told me it needed an o2 sensor at a cost of $800. I purchased a INNOVA Dianogstic reader and it showed a code 'P2098'. Based on that I replaced the Post Cat Bank 2 sensor ($120) and cleared the code. 50 miles later the same code triggered the check engin light.

I don't understand the O-Ring thread since the Post sensor compares readings after gases pass throught CAT to readings before the gases passes through the CAT ; checking the performance of the CAT. Can someone please explain?