OK to answer your question, the O2 Sensor has to be located between the
Exhaust port and the catalytic converter on all OBDII cars. Some have a
second one after the catalytic converter, yours does not I think.
Usually it is located close to the engine on the exhaust manifold
because it requires a certain amount of heat before it will function
correctly. Before it reaches the operating temperature, the system
operates in a specail fail safe mode using factory set perimeters and
will (possibly) run rough due to the fact that it is not real time
adjusting the Air Fuel mixture. For a decent explaination of the O2
sensor, see this link
http://auto.howstuffworks.com/question257.htm.
Now, You have a '99 Sl-2. From my memory, that O2 unit is directly on
the Exhaust Manifold. Open the hood look straight down between the
engine and radiator. The O2 sensor sticks out to the drivers side of
the exhast manifold (the rusty piece of metal coming off the front of
the engine and turning down). There is one wire going into this unit if
I remember ciorrectly, but you need to know the wire count when you go
to the store for a new one. Also, while you're there, borrow their O2
sensor removal and installation tool (if they don't have a loaner for
this go find a store that does, it makes the job easier). The Saturn
wiring snaps off the back ( I think you squeeze the connector) of the
old sensor, you unscrew and then reattach the new sensor.
As someone else wrote, you may not have a bad O2 sensor, I'm guessing
you are seeing code P0153. Check out this link.
http://www.obd-codes.com/trouble_co...sor-circuit-slow-response-bank-2-sensor-1.php
The Code in the computer is just based on what it sees. What it is
telling you in this case is that "I sent the signal for more oxygen to
the intake manifold circuits, and I did not see a corresponding change
in the O2 sensor signal that I expected." The cause can be air getting
into or out of the exhuast manifold, another sensor dumping too much
fuel into the engine, a manifold air sensor that is malfunctioning,
etc... The OBDII codes are nice, but they won't do the work for you,
they just tell you what to start with, you still have to do some
detective work. The first thing I would do is inspect the exhaust
manifold for any cracks, maybe crank the engine and see if you can hear
a sound leak around the front of the engine where the exhaust gases
are maybe leaking. Past that change the sensor and see what happens.
Good luck.
One other note, at 80k that sensor maybe a little tough to remove. If
it is start the engine and run it jsut for a second to heat the exhaust
manifold slight. The metal will expand a little and often unstick a
stuck bolt/sensor/spark plug. Be careful not to get burned.
