O2 sensor connections

[ahlem]

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?

[80stech]

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.

[ahlem]

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.

[oldskewel]

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?



I can see some of the colored wires in the photo there - maybe that will help you figure which is which.

[Clavurion]

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.

https://www.newtis.info/tisv2/a/en/e...sions-control/

[andrewwynn]

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.

[Bmwe5320023.0]

I'm dealing with the same issue.
I had removed all the oxygen sensors when I removed the exhaust manifold.
Now I'm getting a bunch of errors on oxygen sensors.
How exactly do you find what wire goes where?
I tried unplugging one wire from the oxygen sensor but they're all showing the same readings even with one disconnected

Unless I should be looking somewhere else?

[andrewwynn]

Unplug one at a time. Start the engine twice. The one with the SES error for no heater is the one unplugged. Reset code unplug a different one.

You should only have to do this twice. The pre cat and post cat connectors are in very different location

[Bmwe5320023.0]

They originally were in a different location, but as I removed both manifolds, I mixed them up somehow.
Now all the wires seem to reach just fine for pre and post oxygen sensors.
I tried playing around as best I could, and this is what I have now, with everything plugged.
This is from few days ago

Looks like a manifold sensor just went out.

I've been driving around and decided to rescan today again.


So I got 3 errors here
25 Lambda Sensor Heater -Bank 1
18 EWS Signal or Camshaft Sensor (MS43)
79 Lambda Sensor Heater -Bank 1 Post Cat

I erased the codes and let the vehicle idle for 5 minutes.
Then rescanned. Both errors 25 and 79 came back
So I'm very confused by it. I tried replacing pre cat sensor on Bank 1 and even swapping with pre cat oxygen sensor from Bank 2, but the ever present error 25 always remains.
I wonder what does error 79 signify. Maybe the catalytic converter is bust?

I also noted that the voltage is kinda frozen on pre and post cat Bank 1. It does not seem to move at all.
Pre cat Bank 2 is the one that's jumping by a lot, but not others.

[andrewwynn]

When unplugged the computer will use a default voltage