02 sensor questions.. Plz HELP!

[shyshadow48]

Hi,

I have a week trying to research some questions
Online, but so far no luck..
So i have decided to ask toyotanation for help!
I have a 97 Toyota 4runner V6 3.4L automatic transmission. (not a 4wd)
I have a couple of questions:
1. How many sensors does my 4Runner have in total?
2. Does it have an EGR system ( i dont think so, but a mechanic said it does?)
3. What does upstream and downstream sensors mean?
4. It would help to know what pre and post catalytic means!?!?!? A diagram perhaps? People confused me so i dont know what is the pre or post

Sorry theres a lot of questions, but people give me mixed answers.
Any help will be very much appreciated!!

[HATEnFATE]

1. How many sensors does my 4Runner have in total?
Your 4runner has 2
2. Does it have an EGR system ( i dont think so, but a mechanic said it does?)
the 4 cyl does. the v6 does not
3. What does upstream and downstream sensors mean?
Upstream means before the converter(also pre-cat) and downstream means after the converter(also post-cat)
4. It would help to know what pre and post catalytic means!?!?!?
see answer to #3.

I hope this helps you out.

[shyshadow48]

Thank you do MUCH!

This really helped