Oxygen Sensor for 2001 Maxima

Has anyone replaced the oxygen sensors in a newer Maxima? I know there are two, one on the Cat outlet, and one on the air intake (I think the second location is right, but it may be on the exhaust outlet).

The car in question is my folks' 2001 Maxima.

Thanks for any input!

Jacob

On my wifes 2001 SE (V6) there are 4 O2 sensors. 2 on each exhaust bank. One is before the pre-cat (sensor 1) and the other is after the pre-cat. (senor 2, between the cats) They are not to terrible to change yourself and cost about $85. (ordered on-line) You need the 7/8" socket tool especially for O2 sensors. Hope this helps. Just curious... CEL (check engine light) illuminated? If so what code?

since u have 2001 its cal. spec,they have 4 o2 sensors. 2000 are fed. spec with 2 sensors