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Old 06-02-2008, 07:01 PM   #36
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Join Date: Feb 2006
Location: London UK
Posts: 1,234
My Ride: BMW 335i 2007 Coupe
Originally Posted by tony325ci_51 View Post
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 ?
Originally Posted by markovnikov5 View Post
Which POST CAT sensor is for cyl #4-6??
Summer must be here, we had a warm day on Sunday so I got outside under the car and did an oil change.
While I was under there I thought I'd trace the exhaust pipes, finally take some pics and answer this question.

Both post-cat sensors are easy to reach but the Bank 2 sensor (cyl 4-6) will be more fiddly to undo, as the 22mm "sensor socket" (with a slot in it, picture attached) will have to be turned and repositioned just like with a normal spanner. Due to the wires you can't just undo it with a rachet. An open-ended 22mm spanner will be fine for Bank 1 (cyl 1-3) sensor (You couldn't use a "sensor socket" on this, there isn't enough clearance to get a rachet on it.).

(You won't have the advantage of being able to see the view in the 2nd picture. This was taken by holding a small camera in the gap up above the exhaust).

Photos include details of post-cat sensors, and the tools required to replace each:

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Last edited by tony325ci_51; 06-02-2008 at 07:39 PM.
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