2002 LANCER Help needed asap

[nissan4life]

Good day all mitsi lovers
kinda new to the lancer experience.i bought a 2002 cedia had it for at least a week before the check light engine came on.
Had the light checked out and the code said the the catalytic temperature sensor was bad, the mechanic told me was the o2 sensor,so i got one and had that changed.
The mechanic showed me how it was working by the fluctuations on the machine but he is still seeing the catalytic temperature sensor at one steady figure,so he told me more than likely the code would come up again.
In less that a day,here the check light was on again
can any 1 tell me how many o2 sensors are on the 2002 lancer and where are they located or is it the my mechanic has no idea as to whats goin on?
The only sensor im seeing is the one on the top of the exhaust manifold(that is the one i have changed so far)

[mety57]

1st up change yuh name --2 if it,s a gdi it will have 2 --1ontop the other underneath the car if non gdi it will have 1

[nissan4life]

dred i had a b13 beast original condition
i miss tha car
buh anyway i kow about the 2 sensors,got some infor from a fellow tuner
The problem im having is that the previous owner removed the cat below the car and left no track of the rear o2 wire harness,so i really needed to know where does the o2 sensor lead to inside the car so i can trace it back and somehow have it mounted back to the exhaust