Four
There are two of them.
There are 2 oxygen sensors.1 is in front of the catalytic coverter and 1 is located behind the coverter
There are two.
4. Two before the cats and two after.
Two, one in fron of the catalytic convertor and one behind it.
There are a total of four Oxygen Sensors: one in each exhaust manifold near the motor, and one on either side (upstream & downstream) of the catalytic converter.
None in the muffler, one oxygen sensor before and one after the catalytic converter.
the part no. are 64,2387,79856
I think on the 97 it was 3. (On my 99 it is 4) Good luck identifying Exactly which ones you need replaced since two of the 3 are on the same circuit so the bank and circuit error code will result in a "One of Two or Both " guessing game.
Many ppl might say 4 but in reality there are only 2 and it's about $100 a piece if u want to replace them.
on a 3.5, there are 4. 2 are right after the manifold, and 2 are after the pre-cats.
2