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Old 09-05-2020, 09:01 PM
Join Date: Jan 2016
Location: Michigan
Posts: 184
ahlem is on a distinguished road
O2 sensor connections

I am in the middle of a headgasket project.
I smudged the marking tags on the O2 sensor wires and can't identify my markings.
Is there a simple way to define which connectors go to which?
The connectors look alike. They seem to be in pairs.
Anyone have any insight?
I could hope to find an X5 in the junkyard to examine but I don't think there are any at the moment.
Anyone have a photo?
2001 x5 3.0, 1990 e30 M3, 1991 318is, 2002 325i, 2008 335i Dinan stage 3 6 speed,
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Old 09-05-2020, 10:01 PM
Join Date: Mar 2016
Location: Saskatchewan Canada
Posts: 1,009
80stech is on a distinguished road
If you can't get it figured out there is a way from inpa,DIS or scan tool to test if they are connected right with engine running.
1988 325is (purchased new)
2004 X5 3.0 (new to me) 2005 X3 2.5 (new to wife)
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Old 09-06-2020, 05:09 AM
Join Date: Jan 2016
Location: Michigan
Posts: 184
ahlem is on a distinguished road
I have a 2002 325i as well as a Foxwell scanner. Hopefully between the both of them I can make sense of this. I was planning on a simple plug and play.
2001 x5 3.0, 1990 e30 M3, 1991 318is, 2002 325i, 2008 335i Dinan stage 3 6 speed,
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Old 09-06-2020, 12:27 PM
Join Date: Nov 2014
Location: SF Bay Area
Posts: 1,100
oldskewel is on a distinguished road
Here are the downstream connections for banks 1 and 2, on my 2001 3.0i, prior to disassembly.

I took these pics, labeled them with masking tape labels, and then found when putting it back together, that I could tell just from the lengths and the bends in the wires where they needed to go.

So I'd try to figure it out that way - try to put them in their original positions, as the bends in the wires want to go, and hopefully it becomes clear.

Confirming that as you found, the connectors there are interchangeable as they are designed. One of the few (only?) things on the whole car like that.

The upstream sensors are not confusing, right?

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I can see some of the colored wires in the photo there - maybe that will help you figure which is which.
2001 X5 3.0i, 190k miles, AT, owned since 2014
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Old 09-06-2020, 01:02 PM
Join Date: Jan 2013
Location: Finland
Posts: 548
Clavurion is on a distinguished road
Wire colours won't differentiate correct sensors. You can measure directly on DME pins which connector it is. Or if you have diagnostics leave the other unplugged and check if correct lambda signal is missing.

E39 530dA -02 M-Sport Messing metallic
E53 X5 3.0dA -06 Sport Stratus grey
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Old 09-09-2020, 06:33 AM
andrewwynn's Avatar
Join Date: Jun 2015
Location: Racine, WI
Posts: 6,340
andrewwynn is on a distinguished road
I use the second method. Leave one unplugged and look at the live data. You will also get an O2 heater error on the unplugged one.

Trace one of the cords to either of the banks and mark it.

Plug one in doesn't matter which and start the engine.

You will know which bank you plugged in and the scanner will report which bank it is plugged into.

If they matched you guessed correctly if they don't match swap the one you plugged in and pkug in the other.

Same method for pre cat though I think the length and position of the wires makes it easier to tell the banks.
E53 / M54 2001 3.0i gas LHD (pair of them: his & her)
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