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General E46 Forum
This is the place to get answers, opinions and everything you need related to your E46 (sedan, coupe, convertible and wagon) BMW!

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Old 07-18-2008, 01:20 AM   #1
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o2 sensors...how many?

How many o2 sensors are there in an E46? Ive read 4 and Ive also read only 1. I am losing crazy gas (20 miles for every 1/4 miles). And the engine service light is on. I now have 100,300 miles.
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Old 07-18-2008, 01:21 AM   #2
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4 I believe, 2 on the headers and two behind the catalytic converters.
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Old 07-18-2008, 01:26 AM   #3
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4 is correct.


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Old 07-18-2008, 02:24 AM   #4
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Old 07-18-2008, 02:27 AM   #5
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^ yup. good diagram
Originally Posted by VaderDave View Post
I'm having a hard time imagining any set of responses that ends with anyone expressing admiration for Marshmallow.

Perhaps you should stop responding. It's a no-win for you here. :dunno:
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Old 07-18-2008, 07:09 AM   #6
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Just did mine a few weeks ago and the 02 sensor tool that I had wasn't tall enough. I did get the pre-cats our with the use of a crows foot (that was easy) and the post-cats out with a wrench. I had 110K and haven't noticed a difference in anything. I sugest you remove one at a time (post cats) and then install (as opposed to removing both then installing). Reason is you don't want to mix what holes they need to go to.
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Old 07-18-2008, 12:07 PM   #7
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And why haven't you check for codes?
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Old 07-18-2008, 12:21 PM   #8
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Originally Posted by OEMguy View Post
And the engine service light is on. I now have 100,300 miles.
You might be wasting time and money just changing things randomly. Read out the error codes from your OBDII ... use PEAKE or Carsoft or PA Soft etc. It will give you an idea on what the problem could be. Also, if O2 sensor is faulting it will give a code such as P0XXX--which will tell which sensor in which bank needs to be replaced.

Good luck.
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