O2 sensor

[Pemilicious]

Hey guys,
I got told my 99 s2000 has two o2 sensors, one in the manifold and one post cat. Is this true? If so what's the difference between the one in the manifold and the one post cat?

[GU357]

yes im pretty sure there are 2 because people refer to the manifold one as the primary sensor and ive heard others referring to needing to replace the rear one which must be behind the cat. not sure why theres 2 though.

might just have the 2nd one there to check the cat is doing its job?


edit:
just did some research, i was correct their are multiple to comply with OBDII(2) and ones further downstream of the CAT are for making sure its working correctly.

[Pemilicious]

Cheers GU357