i have a 2001 ranger v6 3.0. how many upstream O2 sensors are on this truck? I thought there was one. the the parts store insisted there was two. Also where are they located ?

 

From AutoZone.com:

 

Yep 2 at the collector flange and if its FFV its got like three or four or at least mine does.

 

OBD I vehicles(pre-1996) just had the one O2 sensor, 4, 6, or 8 cylinder

OBD II vehicles had one O2 sensor per "bank" on the exhaust manifolds(upstream) and then will have one or two O2 sensors after the catalytic converters(downstream)
The upstream sensors are used in closed loop to help computer maintain correct fuel/air mix
The downstream sensor(s) are to make sure the cat converter(s) are working as they should.

 

yeah i have two behind the collectors then 2 behind each precut i think there called? and the 1 downstream after the two cats its a strange setup on the FFV.

 

we found them . thank you.