Trying to replace two O2 sensors on my 2004 Impala SS. I have a schematic from Auto Zone that shows three sensors before the cat. converter. I can only find one. Where can I get a correct schematis?

you can apply pressure to the sensor while undoing it to force it out or you will have to cut out the thread area and get an O2 sensor bung hole replacement at an auto supply store and weld into place and install a new O2 sensor. bank 1 sensor 1 is located in the front pipe off the manifold that has cylinder #1 on and bank 2 sensor 1 is on the side that cylinder #2 is on like sensor 1. sensor 3 is the one just before the cat.

o2 sensor is by the cat and sometimes there is 2 of them one before and one after the cat id look on the exhaust manifold most likely there is one there

the o2 sensor is located in the exhaust stream-from the exhaust headers, they are usually not more than 18 to 24 inches from the exhaust as it exits the engine-follow the pipes, they are in front of the catalytic converter-if you have a 4 cylinder, you only have one in front of the cat-if you have a v6, you have two. the o2 sensors BEHIND the cat only monitor the efficiency of the cat itself and have no bearing on driveabillity-concern yourself with the front o2 sensors, they control how the vehicle runs-they get 'tired' as they get older, and should be replaced as you get closer to 100,000 miles. It will generally run better and get better gas mileage.

You will have a total of 4 O2 sensors, two on the left (driver's side-Bank 1) and two on the right (passenger side - Bank 2). Sensor 1 is before cat. convertor and sensor 2 after cat. converter. Hope this helps.

Sensor 2 should be in or immediately after the catalytic converter for bank 1, assuming that its true dual exhaust and dual cat.

If was you o2 sensor the code would say o2 sensor bad. Your catalytic convertor may not be heating up enough to make the emission computer happy and is sending a trouble code.

I believe you may have three (3) O2 sensor, (2) of the sensor is on ether side of the exhaust down pipe and some times called up stream O2 sensor, the third O2 sensor know to some as the down stream O2 and is after the Catalytic converter.
The up stream O2 monitors the left and right side banks and sends signals to the ECM to make the adjustments to the injectors to keep the proper air/fuel ratio.
The down stream O2 monitors the catalytic converter and sends signal to the ECM if the catalytic converter has gone bad.
Good luck and hope this helps. If you get it scanned at Auto Zone, they should be able to let you know which O2 has gone bad so as to not change all three. You could always check the wire harness to the down stream O2 for corrosion.

I have a 2002 Impala with 3.8L, and just replaced my Bank1 O2.
It is located between the firwall and the middle of the engine, straight down past the spark plugs. Maybe 12 inches from the top of the engine.
As I recall the plug for the sensor is clipped to a bracket at about spark plug level.
I recommend using the crow foot style wrench to remove and install.

Your car should have two O2 sensors. One will be located after your catalytic converter. The other one should be located before your catalytic converter somewhere between your headers and your cat. Rarely, on some vehicles, there's a 3rd O2 sensor which is located also somewhere between the catalytic converter and the headers.

Under the truck, driver side exhaust pipe, there are 2, 1 is before the catalytic converter, the other is after. They screw into the side of the exhaust pipe.