They are all located in the exhaust system, 2 are between the catalytic converters and the engine, these are also known as "upstream". The other 2 are between the catalytic converters and the muffler(s) also known as downstream.
in the exhaust pipes just before the catalytic converters
4
FOUR
AnswerThere are three O2 Sensors on my 1999 Cougar. Two are located just before the Y-Pipe and are both wired to the drivers side of the Y-Pipe. The other is located just after the Catalyic Converter.Easy to change.
Usually the come in pairs. So 4 seems most likley.
Need a little more information. there are a number of reasons why your cougar would run rough. Anywhere from the mass oxygen sensor to the idle control sensor, oxygen sensors and on and on.
Mine is an automatic and it has 3. one on each exhaust manifold and one after the cat.
There are two oxygen sensors. One upstream and one downstream. The up stream is located at the front of the vehicle below the radiator and the other is near the cadillac converter. If u go to o reilleys they have a tool just for removing the sensors otherwise u could use a plyers or a cressent wrench to remove them
O2 sensors are always located on the exhaust system.
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
There are two.