What sensor do i get? So many upstreams. Which one do i choose? I dont wanna hafta spend $300 on a $900 vehicle for a sensor! I've replaced it with a generic, "upstream" o2 sensor and I'm still getting the same code. I've already replaced the catalytic converter with a stainless "high flow" and a new downstream sensor so now I just wanna get rid of that annoying check engine light. Help!