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E46 M3 (2001-2006) Engine: S54 - Max Hp: 333 hp at 7,900 rpm / 262 lb/ft at 4,900 rpm
Total Produced: 45,000+ - Years Produced: 2001 to 2006.

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Old Sat, Feb-28-2009, 01:28:34 PM   #1
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Default Which O2 sensor in the pics is the Bank 1/2?

Please take a look at the pictures below. Which O2 sensor goes to bank 1, and
which O2 sensor goes to bank 2? As I am installing new O2 sensors, assume that
they are currently connected improperly, or I otherwise do not know if they are or
aren't connected properly

Now a follow-up question...Does the connection for the rear O2 sensors matter?
In other words, can either post-cat O2 sensor be connected to either side? If not,
which sensor goes to which side in the pic below? Thanks!

2003 JET BLACK ///M3 SMG

Originally Posted by //Ali View Post
What's lesson #2, oh Lord of Ridiculous Posts
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Old Sun, Mar-01-2009, 03:38:42 AM   #2
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With regards to the rear O2s, it's my understanding that they need to replaced in the correct order, however, as you probably know, it would not affect performance either way since they only monitor emissions - you might just throw a SES light.

Also, I think they both have different cord lengths, so they might only reach to correct plug at the valve cover...I would think that the best thing to do is to tag them or remove them one at a time to verify which one goes where...

I've tried to replace the pre-cat O2 sensors on my car from underneath, but have had no sensor is easy to get to while the other is not. I tried a 22mm o2 sensor crows foot socket with an extension, but it was too tall and didn't work in the tight space. I plan on trying a lower profile crows foot socket.

From where did you replace the pre-cat O2s? From above or below? I haven't removed the heat shield from the top, but don't want to if I'm wasting my time. Any help would be apprecited...btw, I have stock headers.

2007 Audi RS4 / GMG Exhaust
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Old Sun, Mar-01-2009, 04:02:49 AM   #3
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Pre-cat O2s, especially for cars that have headers, are a bit of a b*tch. Much easier with a lift.

As for the rear O2s, yes, it matters, but only from a monitoring standpoint; i.e., it will say "bank 2 catalytic efficiency poor" or whatever when it's really bank 1, because you have the sensors reversed. However, as mentioned above, I don't think it's possible/easy to swap them, since the wire lengths differ.
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Old Wed, Mar-04-2009, 12:08:58 AM   #4
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r u installing 4 new ones
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1 or 2, bank, pics, sensor

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Discussing Which O2 sensor in the pics is the Bank 1/2? in the E46 M3 (2001-2006) Forum - Engine: S54 - Max Hp: 333 hp at 7,900 rpm / 262 lb/ft at 4,900 rpm
Total Produced: 45,000+ - Years Produced: 2001 to 2006. at BMW M3 (E30 M3 | E36 M3 | E46 M3 | E92 M3 | F80/X)