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?

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.

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.

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?

Attachment 78795

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

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/

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.

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
https://i.ibb.co/V2yTjrX/20201024-215828.jpg
Unless I should be looking somewhere else?

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

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
https://i.ibb.co/y6qzx14/Screenshot-...orque-Scan.jpg https://i.ibb.co/LtgbqVg/Screenshot-...831-Torque.jpg
Looks like a manifold sensor just went out.

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

https://i.ibb.co/dGJLc2R/20201027-171659.jpg https://i.ibb.co/3ycvpP2/20201027-171711.jpg
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?
https://i.ibb.co/dGJLc2R/20201027-171659.jpg https://i.ibb.co/3ycvpP2/20201027-171711.jpg
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.
https://i.ibb.co/yY3MfDk/20201027-171918.jpg https://i.ibb.co/n1KYWby/20201027-171939.jpg

When unplugged the computer will use a default voltage

That makes sense. Both sensors on Bank 1 (pre and post cat) are showing an error and have the same voltage. Even though they're both connected.
I guess I can try connecting spare o2 sensors to those plugs/connectors and see if I get any readings from ambient air. If not, the wire could be damaged somewhere behind the engine

O2 sensor connections
 

Yep that's the idea. It's not difficult to trace the wires into the e-box where you can determine continuity. I did when I was trying to solve an O2 sensor heater issue that wouldn't go away.

Come to think of it, also how to determine which wire for which sensor. TIS will have the pinout.

I tried disconnecting sensor 1 and 2 on Bank 1 and connecting spare o2 sensors to those connectors without any luck.
The voltage stays the same and the errors come back right away.
I tried tracing wires for bank 1 but they go behind the engine where I can't reach.
Those wires must be damaged somewhere but are they even replaceable or are they part of engine harness?
https://i.ibb.co/Jy3TcML/Screenshot-...347-Torque.jpg https://i.ibb.co/09RnSrJ/Screenshot-...orque-Scan.jpg

It's in the engine harness but you can find which wire isn't working and run your own wires parallel but I would start by finding the pinout from the DME and test continuity on each sensor wire.

What a shame they closed down https://www.newtis.info/

I found DME MS43 pinout though
https://www.ms4x.net/index.php?title...ns_MS43_Pinout

And o2 connectors
https://i.ibb.co/d53hQRL/Screenshot-...934-Chrome.jpg https://i.ibb.co/QYcWs23/Screenshot-...732-Chrome.jpg

I guess the connectors i have to check for continuity with DME are X62101 and X62102
The only problem I can't seem to find the pintout for those connectors who know which DME pins to test for continuity with wich O2 terminals (since there are 4 terminals per O2 connector).

For example pins on DME for bank 1 sensor 1

1 Output [PWM] O2 Sensor Heater Pre-Cat Bank 1 Heated O2 Sensor Pre-Cat Bank 1 B62101
14 Input [0-5V] Signal O2 Sensor Pre-Cat Bank 1 Heated O2 Sensor Pre-Cat Bank 1 B62101
20 Ground O2 Sensor Pre-Cat Bank 1 Heated O2 Sensor Pre-Cat Bank 1 B62101

Now what do they correspond to on the oxygen connector?

After much pain I think I figured it out, at least for sensor 1 bank 1.

Pin 3 of the O2 connector goes to pin 20 of the DME (20 M M_LSV1 Signal ground Oxygen sensor 1 (in front of catalytic converter))
20 Ground O2 Sensor Pre-Cat Bank 1
Black wire (so looks like this wire is simply ground and is not critical, since the O2 sensor is already grounded by being screwed into the cat.

Pin 4 of O2 connector goes to pin 14 of DME E A_LSV1 Sensor signal Oxygen sensor 1 (in front of catalytic converter)
14 Input [0-5V] Signal O2 Sensor Pre-Cat Bank 1
This wire is yellow. Looks like this is where DME is receiving the signal from O2 sensor, which will produce volts depending on temperature. The only think not clear to me is I thought O2 sensor provides between 0 and 1 volts, so why does this day 0-5V?

Pin 2 of O2 connector goes to pin 1 on the DME
1 M T_LHV1 Oxygen sensor heating ground
1 Output [PWM] O2 Sensor Heater Pre-Cat Bank 1
Brown wire
Something to do with pulse width modulation. I think it does something to the voltage.

Last is pin 1 on O2 connector and it goes to pin 8 of the DME fusebox, which is Voltage supply for engine electrical system, fuse 4, 30 amp
Red and white wire
So I figure this is the voltage from O2 sensor to DME, passing through that fusebox?

I guess I can start by checking fuse 4 and then checking resistance between DME connector pins 1, 14, 20 and O2 connector.

https://i.ibb.co/vxvb8p6/20201118-012301.jpg https://i.ibb.co/QPD8NFc/Screenshot-...405-Chrome.jpg https://i.ibb.co/sJHdDn3/Screenshot-...125-Chrome.jpg

The pwm is how the heater runs lower than full power. They are always full power or close eg 97% whenever I watch realtime

I was able to trace all sensors finally, back to where they belonged. Used a multimeter to find the right O2 connector for the corresponding pin on the DME. Marked them with a marker time lol.
They were all messed up, pre and post.
No more active errors, just 3 shadow errors with TEG_DOWN and TEG_UP Inpa codes.

I heard O2 shadow errors don't mean anything and they won't go away. Saw another post with the same issue.

Not sure what shadow error means. Like a pending error that never posts?

I get these shadow errors ALL the time because I changed my O2 sensors to NTKs instead of the OE BOSCH ones. Such a pain in the arse. Hindsight is 20/20, but I wish I knew this before hand and just bought the BOSCH O2 sensors.

But yeah, the shadow codes are the ones that pend but never erase. This is most likely due to the resistance of the heater being different from each MFG. What a pain...

I had continual o2 heater errors until I managed to recalibrate the heater circuit.

I started the car twice with the two replaced rear sensors unplugged. Got a handful of error codes. Plugged them back in, reset the codes, no more codes related to the o2 heaters after that.

Thanks for that clarification! It's good to know it's related to non oem sensors.
I've seen the exact same problem that someone else had but wasn't clear why the pending codes were there.
https://www.bimmerforums.com/forum/s...code-in-shadow
Just same pending codes for the exact same tbing, O2 sensors.
I might just get OEM sensors. My post cat sensors are not even the right ones. The guy who had the car before me installed the wrong sensors, the wires' length is shorter than it should be. They don't make it all the way to where they're supposed to clip. Dunno if it affects functionality at all. I feel like they're from a different bmw model.

Andrew those were the actual errors I take it, not just shadow?
What do you scan with?
INPA has a separate button to scan for "shadow" codes.
If you use Bmwscanner (pasoft) then the shadow errors are yellow, whole active errors are red

I use foxwell for scanning (or think diag).

I was getting actual errors but I suspect the same condition I was having could be giving you the ghost errors. It's easy to try and if it works, may help somebody else down the road.

Does the engine have to actually be "running" twice, or can a simple key on suffice in order to "recalibrate" the O2s?

O2 sensor connections
 

I don't know. I started it I don't think I drove I just wanted to make sure the car tried to heat the O2.

The O2 heater circuit is energised at key on this I know because that's where I power my angel eyes

The actual power to the heater is controlled from the ground side

Andrew I tried testing what you suggested
Right now I have 2 shadow codes for pre cat sensors and one code for post cat sensors (2 up and 1 down)
https://i.ibb.co/hdJXts0/20211007-090735.jpg
I tried disconnecting the front sensor and running the engine.
I got this new error
https://i.ibb.co/mCLKm6Y/20211007-090444.jpg
I reconnected the sensor and tried clearing the errors. Error 25 Lambda cleared fine, but the shadow errors stayed.
I could try changing O2 sensors to OEM (even used ones) to see if anything changes.

Photos too low res to read. Are the shadow errors twisted to the heater ckt? That's what I suggest can be fixed with the recalibrate from running with them unplugged

Those are thumbnails, will open in full resolution if you click on them. I think they won't open properly if you use tapatalk.
I'm not sure what exactly those errors mean
I can rescan with bwmscsnner
I wish I had some extra O2 sensors to test it by replacing them

Ah yes I use tapatalk


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I found two extra O2 sensors for pre cat.
Tried swapping, but nothing changes.
The same shadow errors remain
https://i.ibb.co/WkfxLzH/20211007-160316.jpg
"Short signal to negative"
Not sure if it means anything...
Even if I disconnect the O2 sensor, the error remains.
Maybe it clears itself after however many cycles, I'm not sure.

It's saying that the signal wire is shorting to ground.

Can you chart the output from O2 real-time?

I can see, I think both INPA and bmwscanner have live data.
Not sure about charting.
I know it's saying signal wire is shorting to the ground, but is it really possible 3 wires have a short?

I checked resistance between pin 1 (red and white wire) and pin 3 (black) ground wire. Resistance is 2.090 on my multimeter

If the signal wire is shorting to the ground, it would be Pin 4, yellow wire, which is signal. I'll check resistance between yellow and black

Resistance between ground and signal wires is 043.3 on all 4 connectors
https://i.ibb.co/8Xd6LSw/20211007-170411.jpg https://i.ibb.co/F4dpMRR/20211007-170259.jpg

I think if it was a short, it would be 0

Maybe also worth noting that the pre cat connectors are male, and O2 sensors are female.
While the opposite is true for post cat. Car connectors are female, and O2 sensor connectors are male.

That seems very odd they all read the same. I'm sure you would get an immediate error if it was a dead short. A weak (say 43k Ω) path to ground may give you a shadow error to look into.

You said all four; do you mean feed and signal on both pre-cat? Or signal on post and pre?

This is resistance between pin 3 and 4 on all 4 O2 connectors. So between singal wire and ground.
I would doubt that they are all equally screwed...
Maybe someone can take a measurement on a car without errors?
Or maybe I should go back and measure resistance between pins connector X6002 and each wire at O2 connector, to see if there are any shorts?
I guess all 4 wires should not be making any connections unless connected to the DME. So it wires are different, resistance should be infinite?

Ignore the shadow codes, they are there to indicate that there "has been" a problem and will eventually go away

Still have yet to get my shadow codes to go away. Even if I clear them or whichever, they still remain. I can find two BOSCH O2 sensors for about $70. Thinking I might pull the trigger and order them.

The top two are the same ones I get no matter what.

What are the readings when hot?

Which readings are you referring to, the voltage ones between 0 and 1 volts? With car just idling for 15 minutes?

I re-checked continuity on all wires from DME connector and each of the four O2 connector plugs. Resistance is 0 between the correct pins on DME connector and O2 wires.
Also there's no shorts between the wires.
Basically there's no damage to the wires, or at least nothing that I detected without load and car off.

Voltage plot over time driving constant speed is best.


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