Vehicle in question... 94 FZJ80 I just had it hooked up to a snap-on scanner. Scanner says front o2 sensor, Rich 67, lean 68, Ok cool we know its the o2 sensor but the they are side by side they are left and right but at Toyota dealer they are listed as front and back. So my question is which one is front? Thats kinda lane to list somthing front and back when they are side by side.

Do you have the OBD-II code number? That may be more informative. The official nomenclature is Bank 1 (left side when looking at water pump) Bank 2 (right side). Front is pre cat; rear is post cat. The front and rear sensors are different, but the same on bank 1 and 2 (at least for V8s and V6s)

there are 2 infront of the cat. Its gotta be one of them but the scanner lists it as front bank 1. Trouble is there are 2 sensors there one is listed front and one rear. They are the same toyota PN. Its not the post cat sensor its one before the collector.

BTW 94 does not have OBD2 on cruisers started in mid 95 and is manditory 96 and up

I know it's a PITA and expensive, but replace both of them if the rig has in excess of 150K............
Butch

You're right on needing the number that goes with the code...but a little off on bank 1 and 2.
Bank 1 is the bank that has cylinder 1...that can be on the right, or the left, or the front or back. Now on a I-6..it gets a little more complicated, but not really. Whatever sensor is measuring the exhaust from cylinder 1 is bank 1. The front sensors are oxygen sensors (or air/fuel ratio sensors) and the rear ones are catalyst monitors. I haven't looked at an FJ80 in a while, but if I were guessing, I would bet that it has 2 O2 sensors (front and rear since its an I-6) and 2 catalyst monitors (both after the catalytic convertor). IF you and the parts guys are both talking about O2 sensors and not catalyst monitors, then it should be easy to decide which one is front and rear. Also, check and see if they have a little colored sticker on the wiring...brown or purple or something..that will identify it also. Lastly, if you pull it out, it will have a number on the sensor portion. Good luck.
Do you have the OBD-II code number? That may be more informative. The official nomenclature is Bank 1 (left side when looking at water pump) Bank 2 (right side). Front is pre cat; rear is post cat. The front and rear sensors are different, but the same on bank 1 and 2 (at least for V8s and V6s)