Where and how many o2 sensor's on a 2003 chevy impala?

You have 2 of those and also 2 downstream. You have two banks of cylinders and each one has an upstream o2 sensor and it is located in the exhaust manifold for each bank. Your scan tool should say Bank 1 or Bank 2.

The downstream sensors are after the catalytic converter.

What are the symptoms of a bad upstream O2 sensor? Sensor 1 Sensor 1 is the upstream oxygen sensor. It is the sensor that measures the oxygen content in the exhaust, providing an input to the computer, which determines how to adjust the air/fuel ratio. Sensor 1 is the sensor closest to the engine. Sensor 2 is the downstream oxygen sensor.
Mar 10, 2021

Bank 1, Sensor 1? Upstream or Downstream? - Newparts.com

https://www.google.com/search?q=2015+Chevy+Impala+3.6+upstream+o2+sensor+location

Here's a video. Replacing 02 sensor in chevy impala 3 8

Anrez, your 1991 Chevy trucks O2 sensor could be located in the Y pipe just ahead of converter or in the front portion of the converter.
Check the attached links,instruction and guides, Good luck
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I wouldn't trust anything the Zone tells you. Most oxygen sensor codes are NOT caused by the oxygen sensor. Of coarse, a lot has to do with WHICH O2 sensor code you have. For example, codes P0130,P0131,P0132,P0133, P0134, P0135, P0137, P0138, P0140, P0141, P0171 and P0172, are all valid oxygen sensor/fuel trim codes for a 2003 Chevrolet Impala equipped with a 3.4L V-6 engine.
How you would go about troubleshooting the problem depends on which "oxygen sensor code" you have. Many times, the code can be fixed by simply repairing a leak in a vacuum hose. Quite often, these codes are caused by faulty mass airflow sensors. Then again, every once in a while, the problem is actually the oxygen sensor itself. However, if you go by the knowledge and experience in diagnostics that exists at the Zone, you will be changing an oxygen sensor EVERY time. Then when that does not fix the problem, you will be out the cost of the oxygen sensor, PLUS you will STILL have to diagnose the problem to fix it!

Many people think that all an automotive repair technician does is plug in the "magic box" and replace all the parts that the box (computer) tells them to replace (and the people at the Zone like it that way). TRUST ME, it does not work that way! I WISH it was that simple.

FYI: On Board Diagnostic (OBD) Diagnostic Test Codes (DTCs) NEVER tell you what parts to replace. They are called DTCs because for a trained technician, they tell him which of the hundreds of DIAGNOSTIC TEST ROUTINES to perform in order to diagnose the fault and pinpoint the CAUSE of the problem.

Just a little professional advice from someone who has been diagnosing and repairing cars for about 37 years...do with it as you will.

Chevrolet Impala comes equipped with two oxygen sensors, one on either side of the catalytic converter. Locating the sensors is as simple as crawling under the vehicle.

1. Location

   • The bank 1, sensor 2 oxygen sensor is located downstream of the catalytic converter. To get to the sensor, crawl underneath the vehicle and trace the exhaust pipe until you reach the catalytic converter. Continue to follow the exhaust pipe until you reach the bank 1, sensor 2 oxygen sensor.
     

   Identification

   • You should be able to identify the oxygen sensor as a single wire about 3 to 6 inches long. The oxygen sensor is mounted to the exhaust pipe and should slightly protrude from the pipe.
     

   Function

   • The oxygen sensor is an important part of the vehicle exhaust system. The sensor tests the amount of air in the exhaust stream. It then sends this information to the engine control computer, which determines how much fuel is necessary to maintain a proper air-to-fuel ratio.
     

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Thanks

Hello there are two 02 sensors on this vehicle, 02 sensor 1 {pre 02} is located in the rear exhaust manifold. the second 02 sensor {post} is located in exhaust pipe just behind the cat. converter

There should be an O2 sensor before and after the catalytic converter on your vehicle, so it will have 2 sensors. You'll need a 7/8" open end wrench or an O2 sensor socket to replace them.

It'll look something like this: http://www.carsteering.com/data/all_images/48-01718.jpg

BANK 1 UP STREAM OXYGEN SENSOR LOCATION IS LOCATED ON THE REAR EXHAUST MANIFOLD.

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.

Need a 7/8 open end wrench or a o2 sensor socket. Located in exhaust pipe. The one closest to the engine is Bank 1 Sensor 1. The ones located downstream and known as "Sensor 2"