There are three sensors on this model/year. They are classified as being in Bank1 and Bank 2. Bank one would be the most forward one (visible from inside the hood). Bank 2 would be the one closer to the firewall, and the third one is in your cat.
There are four oxygen sensor in a Maxima 2001. See Nissanhelp.com for a diagram location.
I'm getting terrible gas mileage and i need to know how many are in the vehicle.
one
There are two oxygen sensors on a Nissan Sentra. This vehicle is an ultra-low emission car, thus needing only two oxygen sensors.
The upstream oxygen sensor is located in the exhaust pipe between the exhaust manifold and the catalytic converter The downstream oxygen sensor is located at the catalytic converter outlet
there are two located on the y pipe prior too the pre cats and one more in the rear converter
where is bank one sensor 1 located on 2001 maxima Bank 1 sensor 1 is located at the upper front left hand side of the motor. My 01 20th anniversary edition has 4 sensors. Just recently replaced all 4.
bank one is drivers side, sensor 2 is rear O2 sensor(oxygen sensors are screwed into exhaust pipes)
Go to the dealer and ask one of the guys if they can print it out. It should be one page. If you have California emissions you have four sensors, two in the front and two by the firewall. It's easy just look under your car and you'll see them..
There is 2 oxygen sensors on the 2002 Nissen altima
four
Check this site out, it shows you. http://www.nissanhelp.com/diy/maxima/projects/nissan_maxima_o2_sensor_identification.htm