2d bank O2 sensor?

I have been getting a "Service Engine Light Soon" on my 98 BurB 5.7, I stopped by AutoZone today and had them put the code reader on it and they
came up with the reading that a "Second Bank Oxygen Sensor was bad". Now this vehicle has two 2d bank sensors (after the cat) and two 1st bank sensors (before the cat). They want to sell me four sensors as they suggest I replace all of them, before the others start to go bad.
With the 2d bank sensors costing $69.99 each and the first bank sensors costing $89.99 each for a total of $340.76 incl/tax, and the salesman working on salery plus commission, I wonder why they want me to replace all four?
I am not sure if I want to replace any of them, what do you guys suggest?
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You're all confused. Bank 1 refers to the RIGHT (driver's) side of your motor, Bank 2 refers to the LEFT (pasenger) side of your motor. Each bank has two sensors, one before the catalytic and one after.
So, Bank 1, sensor 1 is driver's side of motor, pre catalytic convertor, and Bank 2, sensor 2 is passenger side of motor, post-catalytic sensor.
The codes the computer generates are SENSOR, not BANK specific, i.e. it'll tell ya which sensor is FUBAR (will look like this: "PO###). So, get the codes re-read, get the EXACT code<s> and post them here. We can then tell ya which sensor<s> need replaced. Do NOT replace them all as this is a complete and utter waste of money.
Doc

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I obtainned and use OBD-software and put oxygen sensors on the graph display, then stat the engine and observe them in the graph display. I think only the preconverter sensors are used for fuel calculations, the postconverter are not. Once on anothe vehicle, the sensor 11 was bad, always .1 volts on it, but with time as computer used that sensor output and added more fuel to the mixture, the other 2 sensors in time setled at .9 volts, so it looked like all 3 are bad. Replacing only one, (bad) fixed the problem.
Ziggie

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pre-converter sensor is used for fuel delivery
post-converter sensor is used to monitor converter efficiency

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Next time, read the little orange code scanner more carefully. It tells you *exactly* which sensor it's having an issue with.
There's Bank 1 Sensor 1, Bank 1 Sensor 2, Bank 2 Sensor 1 and Bank 2 Sensor 2. Each of these 4 different codes will tell you exactly which one. Bank 1 is the side of the engine with the No. 1 cylinder. (in your case, the driver's side). Bank 2 is the other side. Obviously inline motors won't have this. Sensor 1 is the first in the series (closest to the engine), and they are numbered sequentially towards the back of the vehicle.
And another thing - the folks at Autozone *DON'T* work on commission. We're strictly hourly rate, which at this time, sucks hardcore.
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you should only replace the one which is bad. it may also be caused by a catylitic convertor that is not cleaning the exhaust gases if it is a post-catalyst sensor. this is an example of a ripoff. unlike the spark plug issue i read earlier in this NG. best of luck -impala
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