272D looking for wiring gurus

[Scrippy]

So I recently got a check engine light. Scanned with ISTA and it’s 272D (O2 sensor heater after cat bank 2). I swapped bank 1 & 2 post cat sensors and the issue stays with bank 2. I have all 4 new sensors sitting on the shelf. I even threw my (2) new post cat sensors in bank 2 and no change. My question is…..from DME on passenger side cowl how do the 4 wires get down to the sensor? Can the wires be replaced with engine in or am I hating life? I want to inspect the wires all the way point to point and find the issue. I have a screen shot of the INPA live voltages and you can see that bank 2 is 249mV lower than bank 1. Swapping sensors and trying my two new sensors yields roughly the same mV desparity. I have already replaced the exhaust collector ring gaskets on both sides. My old gaskets were only 2 years old and looked just fine. Does anyone know the wire path? Could this be a leak at the header gaskets? I don’t hear or perceive any exhaust leak but I’m open to ideas here. Thanks in advance!

[amrazM]

The rear o2s are part of the transmission harness. Measure resistance across the lines before you replace it. does this car have a tune on it? are cats installed?

[Scrippy]

Stock, no tunes. What pair? The black grey? It’s black grey for power output on the sensor but looks like on the car harness the colors are completely different. I can figure that out easily. Thanks for the advise and reply too.

[Scrippy]

Both wire pairs of harness on both harness plugs are open, zero resistance. Both O2’s show 8.4 ohms on white pair and open on black grey pair.

[Scrippy]

I think it’s my bank 2 cat. Both cats have an inlet temp around >300 degrees. The bank 1 sides outlet is around >360. Bank 2 outlet is >315. This may be expensive to rectify with X-pipes costing greater than 7k.

[RocketyMan]

Originally Posted by Scrippy

So I recently got a check engine light. Scanned with ISTA and it’s 272D (O2 sensor heater after cat bank 2). I swapped bank 1 & 2 post cat sensors and the issue stays with bank 2. I have all 4 new sensors sitting on the shelf. I even threw my (2) new post cat sensors in bank 2 and no change. My question is…..from DME on passenger side cowl how do the 4 wires get down to the sensor? Can the wires be replaced with engine in or am I hating life? I want to inspect the wires all the way point to point and find the issue. I have a screen shot of the INPA live voltages and you can see that bank 2 is 249mV lower than bank 1. Swapping sensors and trying my two new sensors yields roughly the same mV desparity. I have already replaced the exhaust collector ring gaskets on both sides. My old gaskets were only 2 years old and looked just fine. Does anyone know the wire path? Could this be a leak at the header gaskets? I don’t hear or perceive any exhaust leak but I’m open to ideas here. Thanks in advance!

Here is a wiring schematic that you requested since nobody else provided you with one yet. The bank 2 post-cat O2 is a bit of the worst because it has two splices for the supply AND ground to the heater element.

I suspect wiring here. In order to actually verify this, you would need to load both circuits and determine what the voltage drop is if there is compromised wiring; ergo a bad splice. This points to bad wiring because the heater element should always be roughly the same for post-cat O2s because they're both on the same circuit. Hopefully this makes sense for you and you can take it from here to electrically test the circuit.

As an FYI, the e-box locations for those connectors I referenced--I would take them with a grain of salt and actually verify you have the right connector. For instance, X6021 and X6200. Also, I cannot determine where exactly those splices are.

[Scrippy]

Originally Posted by RocketyMan

Here is a wiring schematic that you requested since nobody else provided you with one yet. The bank 2 post-cat O2 is a bit of the worst because it has two splices for the supply AND ground to the heater element.

I suspect wiring here. In order to actually verify this, you would need to load both circuits and determine what the voltage drop is if there is compromised wiring; ergo a bad splice. This points to bad wiring because the heater element should always be roughly the same for post-cat O2s because they're both on the same circuit. Hopefully this makes sense for you and you can take it from here to electrically test the circuit.

As an FYI, the e-box locations for those connectors I referenced—I would take them with a grain of salt and actually verify you have the right connector. For instance, X6021 and X6200. Also, I cannot determine where exactly those splices are.

Thank you for this! I really appreciate it. Prolly dig in to this next weekend. I’m worried it is my actual bank 2 cat though. Using a torch and ohm meter I can confirm my in car sensors are good as well as my spares. They are all reacting to heat the same. When I use my infrared thermometer I have a lower temp on my bank 2 cat exit when compared to entry. A nex X pipe seems to be 7k or higher.

[spammysammich]

Pull your sensors and put a bore scope in there to examine. Great excuse for purchasing a bore scope. Handy every where from checking cylinders for bore score to chasing oil leaks.

[Scrippy]

Originally Posted by spammysammich

Pull your sensors and put a bore scope in there to examine. Great excuse for purchasing a bore scope. Handy every where from checking cylinders for bore score to chasing oil leaks.

I own a scope. What would I be looking for? Like a build up on the cells I guess.

[spammysammich]

Melting. Especially on the precat side.

[darren p.]

Originally Posted by RocketyMan

Here is a wiring schematic...

This is great, were do you get these images from?

[Scrippy]

Got the flu and have been down this last week. I finally got to dig back into this issue. I followed the diagram RocketyMan provided and started at the ECU with my meter. I pulled the plug that connects the O2 after cat wiring to ECU. So on pin #5(white) I get 12-14vdc which is bank 1 after cat O2. On pin #6(white/purple) I get nothing which is my bank 2 after cat sensor. This confirms a wire problem. Not sure how I’m going to resolve this. I’ll probably have to bite the bullet and take the car to my dealer. I have no means of dropping the motor and front subframe to access this wire on top of the trans. Bummer!

[RocketyMan]

Originally Posted by Scrippy

Got the flu and have been down this last week. I finally got to dig back into this issue. I followed the diagram RocketyMan provided and started at the ECU with my meter. I pulled the plug that connects the O2 after cat wiring to ECU. So on pin #5(white) I get 12-14vdc which is bank 1 after cat O2. On pin #6(white/purple) I get nothing which is my bank 2 after cat sensor. This confirms a wire problem. Not sure how I’m going to resolve this. I’ll probably have to bite the bullet and take the car to my dealer. I have no means of dropping the motor and front subframe to access this wire on top of the trans. Bummer!

Thanks, Scrippy, for reporting back and posting a picture of x6200.

Couple of Q's:
1. How are you measuring the voltage? Are you back-probing with x6200 plugged in?

2. Did you try clearing the code to see if supply voltage would return?
These are FET controlled--meaning the DME can turn that circuit off.

3. Did you try testing continuity on pin 5 right to the O2 connector?
This would be a good double-check scenario.

4. Did you also try investigating the DME connector, X60105?
Does x6200 have continuity to the DME connector? 6 to 44?

[Scrippy]

Originally Posted by RocketyMan

Thanks, Scrippy, for reporting back and posting a picture of x6200.

Couple of Q's:
1. How are you measuring the voltage? Are you back-probing with x6200 plugged in?

2. Did you try clearing the code to see if supply voltage would return?
These are FET controlled—meaning the DME can turn that circuit off.

3. Did you try testing continuity on pin 5 right to the O2 connector?
This would be a good double-check scenario.

4. Did you also try investigating the DME connector, X60105?
Does x6200 have continuity to the DME connector? 6 to 44?

1-I measured that voltage with the connector unolugged. I put positive lead on 5 and negative lead in engine bay ground. #5 gives the 12-14VDC. #6 gives nothing.
2-I did try clearing error with ISTA but it still shows existent.
3-Did not run continuity from connector to O2. I will get the car up and try that soon.
4-I did not do anything from connector to ECU. All does look good however when I unplug the connector. No corrosion or bent pins.

Got any ideas other than continuity check from plug at ECU to O2 plug?

[RocketyMan]

Originally Posted by Scrippy

1-I measured that voltage with the connector unolugged. I put positive lead on 5 and negative lead in engine bay ground. #5 gives the 12-14VDC. #6 gives nothing.
2-I did try clearing error with ISTA but it still shows existent.
3-Did not run continuity from connector to O2. I will get the car up and try that soon.
4-I did not do anything from connector to ECU. All does look good however when I unplug the connector. No corrosion or bent pins.

Got any ideas other than continuity check from plug at ECU to O2 plug?

Gotcha. Thank you for clearly answering those.

I would still suggest checking continuity from the DME connector to x6200 just to make sure the issue isn't there.

When you get a chance to check the continuity from the O2 plug to x6200, you'll most likely need a spare wire extension to check the loop. The purpose of this is to isolate where the issue is as it might be on pin 6 or even further up the chain.

[Scrippy]

So good to know the issue but sucks that the motor and trans will have to come down to fix it properly. For now I will run a temp wire to get back the sensor functionality but it was in fact that white/purple. That was the wire I was not getting my 12vdc on a few posts back. It’s all chewed up. While doing a continuity test from ECU to the O2 plug, I did not get cont on that white purple so I pulled it and about 9” came out all chewed up.

[Scrippy]

Ran a temp wire to replace the broken wire. Cleared error and all good now. Does anyone know if I can gain access to the wire harness by removing the center counsel or anything like that?

[RocketyMan]

Originally Posted by Scrippy

So good to know the issue but sucks that the motor and trans will have to come down to fix it properly. For now I will run a temp wire to get back the sensor functionality but it was in fact that white/purple. That was the wire I was not getting my 12vdc on a few posts back. It’s all chewed up. While doing a continuity test from ECU to the O2 plug, I did not get cont on that white purple so I pulled it and about 9” came out all chewed up.

Thanks for reporting back with a picture! Confirms where the problem was exactly. But very interesting how the wire was damaged. I would be curious if that wire wasn't the only one. Maybe you can share some insight in that?

As for your Q, the center console will not gain access to this area as this would be a very tight squeeze. The front O2 sensors run down towards the rear-right of the engine. I'm not sure the exact route of the rear O2 sensors.

[Scrippy]

So I did get a view of the damage with my scope. The plastic loom is bashed up. I presume this happened the last time my dealership took the motor and trans out and the wire finally vibrated apart. I recon they banged shit around putting the car back together and pitched the wire on the trans tunnel. The dealership is the only shop I use when I can’t do myself. I was chasing a vibration on hard acceleration that ended up being my constant velocity joint. They threw a harmonic balancer, dual mass flywheel and other goodies at it which required tranny out. None of it fixed the vibration until I made them look at the driveshaft and nothing else. All reasons why I cringe thinking about them doing work for me. I’m being quoted $4700 just to get trans out for me to fix the wiring myself and then have them put it back. I may just attempt to lower trans myself at this point.

[RocketyMan]

Then I totally would chalk this up to dealer responsibility for the failure. They were the last ones in there, and nothing would randomly chew up the harness like that.

I'd be furious--especially knowing the dealer was the last one in that exact area.

[Scrippy]

Yeah but that service was over a year ago. Nothing I can do now. All I can say is, be warned about Autonation BMW of Valencia. I’ve had 3 BMW’s until now and I’ve had issues with all 3 and the work they’ve performed at that dealership. I am really considering just purchasing a two post car lift to avoid using them anymore. Having a lift would really make me self sufficient. My garage has an 8ft ceiling, so I could probably lift the car up at least 4ft. That would be enough to drop the power train on a low rolling table.

[RocketyMan]

Still! If it were me--i would at least have a conversation with them about it.
I would try and see if you can get more room by tilting the engine back by removing the transmission crossmember. It'd help with the plenum removed. I think you can get by with just a simple exhaust drop, driveshaft removed, heatshields removed, reinforcement plate removed, plenum removed, and see if you can tilt to get clearance.

At any rate, I'm glad you found the issue and reported your findings.

Keep us updated on the repair