OXYGEN SENSOR LOCATION 91 GMC PICKUP - 1991 GMC Sierra

SOURCE: need to know where sensor 1 (oxygen sensor) on bank 1 is located

It would be on the left header pipe as you sit in the truck. Its the sensor in front of the cat

SOURCE: where are the oxygen sensors located?

There will be one located before, and one located after the catalytic converter for each exhaust that you have

SOURCE: i have a 2002 gmc sierra 1500, need to change the

There are several located within the exhaust system(PIPE)You need to know witch one.

SOURCE: where is the oxygen sensor

there should be 2,both are in the exhaust 1 behind the cat.converter & 1 upstream
if the truck has dual exhaust it may have more than the 2.if your reading codes it will
list them as bank 1 sensor 1 or 2. sensor 1= upstream 2 = behind cat
good luck

SOURCE: I would like to know

From my research, there are multiple O2 sensors on the exhaust system. They can be found near the catalytic converter, before and after it. O2 sensors are easy to find by the wires sticking out of the exhaust system and the mounting bungs for them.