How to locate and change the oxygen sensor on an audi a6 2002 front passengers side?

It's the front sensor on the passenger side. Take care.

Referencing oxygen sensor or O2 sensor or 'lambda sensor':

B1S1 is 'bank 1', which is the passenger side cylinder bank on a V6 or V8.

S1 is the 'upper' or 'upstream' sensor, closest to the cylinder.

On the back side of the motor follow the manifold down to the exhaust pipe and then it is the 1st sensor you come to.

The 1999 5.3 V8 engine had 4 oxygen sensors. There are two catalytic converters on this engine, one on the driver side of the engine, and one on the passenger side of the engine. This is important to know, as the number of oxygen sensors is directly related to the number of catalytic converters on the vehicle. Driver side is referred to as Bank 1, passenger side is referred to as Bank 2. This is very important to know when looking up replacement oxygen sensors. There is one oxygen sensor in front of, or before the catalytic converter, usually referred to as a pre-catalyst O2 sensor. There is also one behind, or after the catalytic converter, usually referred to as a post-catalyst oxygen sensor. So, you have two oxygen sensors on Bank 1, and two oxygen sensors on Bank 2, for a grand total of 4 oxygen sensors.

On all cars, the bank 1 is where the first piston is...Your firing order on that car which is the first piston...Buy a chilton or a repair manual for your car and it will tell you which firing order your motor has....Its usually on the right hand side...Passenger side...Rule of thumb if you look at the spark plugs the one closest too you is usually the first piston....Bank 1 is located on the same side as the first piston...I hope this helps...

O2 sensor is after catalytic convertor and only one and most never goes bad, just needs cleaned.

Oxygen sensors are always numbered like this:

Bank 1 sensor 1
Bank 2 sensor 1
Bank 1 sensor 2
Bank 2 sensor 2

some manufacturers use a kind of shorthand that reads different, but means the same thing:
Sensor 1/1 or O2s 1/1
Sensor 2/1 or O2s 2/1
Sensor 1/2 or O2s 1/2
Sensor 2/2 or O2s 2/2

Bank 1 is always the side of the engine where cylinder number 1 is located and, of coarse, Bank 2 is the opposite side.
On a 4 cylinder engine, there is only 1 bank and it is always referred to as Bank 1.

Sensor 1 is always the upstream sensor (The one located BEFORE the catalytic converter)
Sensor 2 is always the downstream sensor (the one that is located AFTER the catalytic converter.

Most GM engines have #1 cylinder located on the left bank, (or Driver's Side) of the engine,

So, the answer to your question would be that you are looking for the sensor located before the catalytic converter on the right (or Passenger Side) of the truck.

Bank two oxygen sensor, located in front of the catalytic converter on the passenger side has failed. The actual code reads: P0151 - Heated Oxygen Sensor (HO2S) Circuit Low Voltage Bank 2 Sensor 1.

The oxygen sensor is located in the exhaust right before the catalytic converter. It is a 3-wire type sensor. You will need to use an oxygen sensor to get it out, and a handy tip is to spray it with some penetrating liquid, then let it soak for 20 minutes before removal.

passenger side of manifold, before the catalytic converter. this system may have more than one on the frontside of the cat.