Need to replace o2 sensors on 2001 infiniti I30t

[crand580]

Hi everyone! This is my first time posting on here. I have been reading info on here for quite awhile though. SO here is my problem. I failed emissions-says catalyst is below threshold bank1 and 2. I already changed oil, new platinum tipped spark plugs, new K&N air filter. SES light still on. My assumption is to change the o2 sensors. My repair manual says there are only three and I can only see three. The parts strore says there is four. Anyways, I need to replace these by myself and need to know in detail how. Can anyone help me???? They look easy, but I need step by step instructions or a link. Thanks. BTW my car has 150,000 miles on it.

[maxhopper]

Welcome to NICO.

Location of O2s.zerothread?id=120838

Directions on how to change O2s.http://www.nicoclub.com/articles.php?id=157928

[Mike G]

Are you going to replace all four or just the ones giving you trouble? You can have the codes pulled from the ECM, but I recall for some reason that the cat inefficiency refers to the sensor 2 position. For what it's worth, my car tosses these codes when I run the cheap 85 octane gas...--Mike