4 o2 sensors?

[muhafuha]

theres should be 4 O2 sensors on a 98 svt right? im looking for the one before the rear one (#3 of 4) scanner said it had a bad heater so i have to replace it.. i changed out the one on the rear bank located right under the car but i cant seem to find any O2's other than the front and rear exhaust !

 

[Pole120]

There are 4

(2) in front exhaust manifold, one before and one after the pre-cat
(1) in the rear exhaust manifold before the pre-cat
(1) in the y-pipe