Whats the part number for this sensor and isnit the sensor located on the back header? Or is it somewhere else

 

Plenty of info available, but had some time.
Upper sensor before cat rear/firewall side.

OEM
22690-2Y920 Production Date: 04/1999-04/2001 VQ30DE

22690-2Y921 Production Date: 04/2001-06/2001 VQ30DE

22691-8J101 Heated Oxygen Sensor VQ35DE

Plenty of aftermarket units available, just got to make certain:
rear, upstream, and also length of wiring:

WALKER PRODUCTS 25023133
NTK 24619
DENSO 2343111
STANDARD MOTOR PRODUCTS SG643
ACDELCO 2132902
HITACHI O2S0039

 

Ok so it's the second upstream that o2 sensor is very long when i look at it from the back of the engine

 

You know how the 4 sensors are are in front of the engine bay is it the one all the way to the right

 

This should help:
https://maxima.org/forums/5th-genera...on-issues.html

 

Im buying this one