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O2 Bank 2 Sensor 1, which one?

77K views 25 replies 12 participants last post by  OkieT 
#1 ·
Question for you guys: which O2 sensor is the Bank 2 Sensor 1? I know it's the Pre-Cat sensor, but which one is it. There are two, one closer to the firewall and one closer to the front of the car.

Can anyone tell me which O2 Sensor is Bank 2 Sensor 1?


Thanks a lot.
 
#6 ·
You don't say what your mileage is, but if you are at the point where you're replacing the O2 sensors, do yourself a favor and do them both at the same time. For the $70 or so for the second sensor you'll buy yourself another 100K.
 
#11 ·
The last time I replaced an O2 sensor was on my dad's eclipse, and I bought a bosch universal (you have to splice the wires) for $60 instead of the $100 for the one with the connector.

When I had to replace the second one (and I did have to replace the second one shortly after), I found that autzone had the bosch one with the connector for $75. Not sure if they've dropped in price or what, but I was pleasantly surprised to see that autozone had a really good price for something I could pick up right away.
 
#15 ·
Hello Sdbimmer !! Thank u fo the diagrams!! I have the same problem, now I can see clearly which one i need but most likely I might have to buy both . Is it true that both top 2 sensors are the same . One out of two dealers told me that the pre cat sensors are the same ..well to my 08/528xi ..? the other dealer told me differently so I took non of their advice !!
 
#18 ·
#2 is (Bank 2, Sensor 1) and for your car it is a little shorter than the sensor in the front. they are basically the same sensor. If the shop doesn't have #2, you can probably just buy #1 to put into #2 position. That's probably the reason why the shops are telling you both answers.
 
#20 ·
You're welcome. Good luck on your fix. For me, I only replace just that one bad sensor. These sensors are expensive, so I only replace just one. It's been running great for the past couple of years. I don't think replacing one bad sensor affected the gas mileage either, so I'm ok with it so far.
 
#23 ·
Bank 1 is cylinders 1 to 3, so looking at the exhaust manifold, it is the pre-cat O2 sensor closest to the radiator.

Try looking up your car at www.realoem.com using last 7 digits of VIN, but the diagram below suggests both pre-cat O2 sensors (#1) are the same length wiring (320mm):
 
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