E46Fanatics - View Single Post - DIY: Post-Cat O2 Sensors + Pre-Cat O2 Sensors
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Old 06-26-2008, 11:43 PM   #40
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Join Date: Feb 2008
Location: Castle Rock, CO
Posts: 37
My Ride: 2001 325xi wagon
Originally Posted by tony325ci_51 View Post
Great write up, very useful but one thing missing.

Error codes refer to bank 1 or bank 2. As I understand it, bank 1 is cylinders 1-3, bank 2 is cylinders 4-6.

Although when you get into the job you can probably work it out (am I right assuming cyl 1 is at the front and cyl 6 at the back ?), it would be really useful if the sensors and connectors in the pictures had been labelled as to which was the bank 1 or bank 2 post-cat sensor and plug. If I get a bank 1 error (P0420 - cat bank 1 below efficiency actually, but the car's passed an emission test in the MOT so I suspect post-cat sensor at fault, not cat) I'd like to know which sensor to look at (so I know in advance whether it's the "easy" one or the "hard" one I'm looking at changing).

Can anyone help with that info ?

Hey Tony, I have the exact same error on my 03 M3 saying htat efficiency for bank 1 is below threshold. Did you fix your problem and did the light go off? I was just wondering if you could help me out because I'd like to do it myself. Was it a post-cat sensor and did you just have to replace one? Any help would be appreciated. Thanks.
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