so my down stream 02 sensor is out. i know on some cars the downstream sensor does nothing more than flick your check engine light on but others will make the car run smoother and get better gas MPG and more horses. so does anyone know if the downstream 02 sensor on my 96 civic is worth replacing for 69 bucks or just buy one of those bypass sensors for ten bucks. if its going to help my car out at all ill replace it. thanks for the input.