i replaced mine this weekend... i have a 92 and it was around 72 from bavauto... pre 96s only had one o2 sensor... post had 2... i see you have a 97 so i would make sure before just ordering which one you really need...
and oh one more thing... if you are going to do it yourself, there is a special tool to remove the sensor... it's only like 10 bucks... trust me, it will come in very handy...
Rex the front two O2 sensors in the '97 328i you have should take care of it. One heated BEFORE each Cat, and one HEATED after each Cat. You can replace your front sensors and reset the light and you're probably good to go.
On the OBDII cars the O2 sensors are heated due to their operating design. On the older OBDI cars the O2 sensors are not heated and much less accurate.
The front O2 sensors is exposed to all the dirty exhaust gases, that's why they die at a much higher rate than the rears. Its actually rarely the rear sensors unless their heater elements just fail. The rear sensors get to breath clean exhaust gases AFTER they've gone through the Cat Converter. They really only change readings if the Cat has failed.
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