O2 sensors are always located on the exhaust system.
There are two.
There are two.
The oxygen sensors are in the exhaust pipes on most models.
Your Villager has only one O2 sensor located on the front catalytic pipe before the converter. You should be able to look down between the engine and radiator and see it.
Both oxygen sensors are in the exhaust pipe, one under the front of the engine, one roughly under the passenger seat are.
I wasn't aware that there was a middle oxygen sensor. I have a 1997 Villager that was vandalized and the catalytic converter and O2 sensors were stolen. From what my mechanic tells me and Auto Zone there are only 2 sensors, one in front of the catalytic converter and one behind it.
There are two oxygen sensors, one in the exhaust near the engine, one in the exhaust pipe after the second converter, roughly under the passenger seat on OBD-II vehicles.
There are two sensors, one in the exhaust pipe at the front of the vehicle, one after the second converter under the passenger seat area.
in the exhaust pipes just before the catalytic converters
There are a total of ( 4 oxygen sensors ) according to the engine wiring schematic for the 1997 Mercury Mountaineer in my Haynes repair manual ( 2 oxygen sensors are " upstream " sensors used by the PCM to adjust the air / fuel ratio of the engine ) ( 2 oxygen sensors are " downstream " sensors / catalyst monitors )
Four