Don't know what your original reading was, but the O2 sensors before the cats moniter how the engine is running and the O2 sensors after the cats moniter how the cats are performing.
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 sensors all over the engine, transmission, chassis, etc.
there are 4 o2 sensors
two
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
A 1994 Explorer has 2 oxygen sensors, they are either screwed into the exhaust manifolds at their outlets or into the ehaust pipes near the engine.
4
2
There are 2 oxygen sensors.
( 2 ) oxygen sensors ( I BELIEVE they are in the outlet areas of the exhaust manifolds )
Reading Sensors..