Location of the O2 sensor

[Rocky]

Got a quick question. (repost from sister site)

I know the 1997 C36 as well maybe the C280 have a 3 piece exhuast. The Headers is the first piece. The cats ans resonators are one long piece. Then you have the muffler as the third piece.

My Question would be is the pre cat O2 sensor on the headers piece or the cat and resonator piece of the exhuast?

[manny]

Pre-cat O2 means closest to the engine.
Post-cat O2 means after the catalytic converter. ;)