I'm not a mechanic but looking at the engine wiring schematics , for 1991 and 1992 models , I only see ONE heated oxygen sensor. ( which happens to have a 15 amp fuse in location # 18 of the fuse panel ) it is referred to as an upstream o2 sensor. I'm not sure exactly where it is located, but it is threaded into the exhaust pipe close to the engine or one of the exhaust manifolds.
That would depend on what year of Ford Explorer and which engine you have ( my 1995 Ford Explorer with the 4.0 liter OHV , V6 engine has ( 2 oxygen sensors )
there are 4 o2 sensors
On a 1995 Ford Explorer : There are ( 2 ) oxygen sensors ( I believe there is one sensor in the outlet of each exhaust manifold )
My Chilton repair manual - engine wiring schematic shows ( 2 ) heated oxygen sensors for the 1993 Ford Explorer
how many o2 sensors on a ford e350 van 2003
My 1995 Ford Explorer with 4.0 L OHV has 2 oxygen sensors (Helpfull)
According to my Haynes Explorer Repair Manual : A 1997 Ford Explorer , 5.0 liter V8 engine has ( a total of 4 oxygen sensors )
There are 2 oxygen sensors.
A 2001 Ford Explorer Sport , with the 4.0 liter Single Over Head Cam V6 engine should have ( 4 oxygen sensors )