Help Diagnosing O2 Sensor Codes

Hi all,

I recently installed a BW forward X-pipe with 300 cell GESI cats in the secondary position. Prior to doing so I was not getting any SES lights although I hadn't scanned it for any codes at the time. Rear section is Corsa. After the X-pipe install, the SES light did pop on (as expected with no tune). I got a bunch of codes for O2s which I assumed were due to the lack of primaries. There were some others unrelated to the O2s. I cleared the codes, loaded up a tune that updated the DME to 240e and a day or so later, the SES light came on. I checked the codes again and some of the ones I had prior to the tune came back.

These are the codes I was able to find info on with links and some notes:

2751 Lambda sensor error pump current cable VKAT bank 2
https://www.m3post.com/forums/showpost.php?p=15249062&postcount=18
Pre-cat O2 sensor bank 2?

2743 Lambda sensor heater resistance diagnostic VKAT bank 2
https://www.m3post.com/forums/showpost.php?p=15533725&postcount=61
Pre-cat O2 bank 2?

2B59 Coolant thermostat monitor
https://www.m3post.com/forums/showpost.php?p=15175604&postcount=2
Check coolant sensor is good, replace if necessary. Replace thermostat?

2742 Lambda sensor heater resistance diagnostic VKAT bank 1
http://wiki.rcollins.org/core/index.php/MSS60_Error:_2742,_P0135
Pre-cat O2 bank 1?

These are the codes I was not able to find any info on:

2B72 INDEX_122_IGN

274A Lambda sensor pump current assimilation error VKAT bank 1

2725 Lambda sensor electric diagnostic VKAT bank 2

2749 Lambda probe Diag.via ATIC42-device VKAT Bank2

Looking at all this, my inclination is to replace the 2 primary O2 sensors and the coolant temp sensor and/or the thermostat but I don't just like throwing parts at problems, I like understanding the actual issue. The previous owner claimed he paid $650 for an O2 sensor harness repair at 130k miles but I have no knowledge if or when the O2s were replaced. He also claimed other things were replaced which I found was not true or he got ripped off for work he paid for.

I did not replace the exhaust gaskets when I installed the X-pipe so it is possible there is a leak. Would that cause any of these codes?

I reached out to the tuner (Epic Motorsports) this morning to see if he had any insight and am creating this thread to start a discussion about it (I did search all codes) and see what the experts in the community think.

Thanks for any and all help!

Never reuse the crush gaskets they will leak.

My understanding is that you need a tune specifically for the Bimmerworld xpipe.

Never reuse the donut gaskets. Make sure they are installed tightly.

Not sure what would cause a coolant sensor.

your first mistake was not using new gaskets lmao

omgzirra_exe wrote

your first mistake was not using new gaskets lmao

Understood, what was my 2nd mistake? ha! I'm certainly no expert nor do I claim to be but I do learn from my mistakes. They say expert is just someone who has made all the mistakes!

So the consenus is the gaskets. Should I bother with anything else for now or wait and see how it does with the new gaskets?

I don't believe the code for coolant sensor/thermostat is related...that may have been there for a while and from what I was reading, it seems that it may be my thermostat. My coolant temp seems to be fairly cool most of the time (what is normal coolant operating temp?) and I haven't turned the heat on since last winter but vaguely remember it not getting very hot.

It is a BW specific tune btw.

Thanks for your help guys!

As others have mentioned - don't reuse the donut gaskets and just get brand new. If you installed an aftermarket x-pipe make sure to use the correct length bolts when mating it up with the headers. I reused the oem bolts and noticed that my O2 sensors were getting destroyed every few thousand miles because it wasn't closing the gap enough because of the shortened threads of the oem hardware.

Sublivion wrote

If you installed an aftermarket x-pipe make sure to use the correct length bolts when mating it up with the headers. I reused the oem bolts and noticed that my O2 sensors were getting destroyed every few thousand miles because it wasn't closing the gap enough because of the shortened threads of the oem hardware.

Interesting, I did get a new OEM set of bolts and nuts with the donut gaskets but have yet to install them. That seems like what may be happening in my case, if not for also the reused gaskets.

So you'd replace the O2 sensors and they would fail prematurely until you noticed the longer OEM hardware wasn't sealing the aftermarket x-pipe adequately? I will measure the flanges of the OEM X-Pipe and BW X-pipe to see the different thicknesses. Is there room to stack washers on the bolt side to gain back that difference? Is that a bad idea on the header flange with the heat?

heater resistance code usually points to a failed o2 sensor, but like others have stated if there is an uncontrolled air leak that would what you need to fix beforehand.

amrazM wrote

heater resistance code usually points to a failed o2 sensor, but like others have stated if there is an uncontrolled air leak that would what you need to fix beforehand.

Thank you, that is helpful.


So I replaced the donut gaskets on Saturday finally and used the OEM nuts and bolts and cranked them down tightly. I confirmed it is NOT an issue of the OEM bolts not closing the gap enough, I'm not running out of thread on the bolts and Bimmerworld recomends new OEM nuts/bolts for the installation.

I cleared the codes and one of them came back immediately, even without restarting the car:

2725 Lambda sensor electric diagnostic VKAT bank 2


Drove the car about 50 miles or so since Saturday and the only other code that came back was:

2B59 Coolant thermostat monitor

I'm not sure if more codes will come back the more I drive it but am not going to wait to find out and am ordering 2 new O2 sensors, a coolant temperature sensor and a new thermostat and see how I do after that. Are the cheaper Bosch O2 sensors on FCP okay or should I go for the genuine BMW sensors (likely made by Bosch)?

2725 - Swap the sensors and see if the error follows. Bosch sensors are fine, they're OEM.

Redd wrote

2725 - Swap the sensors and see if the error follows. Bosch sensors are fine, they're OEM.

After more driving, still only these 2 codes. Parts are arriving by 7:00pm today so we shall see. Not sure I want to bother swapping but would be good piece of mind but I got 2 new sensors anyway. I guess I'll change bank 2 first and see if the code goes away.

Should I be just clearing the codes or should I also clear the adaptations as well? I guess over time the adaptations will update with the new sensors but may be quicker to clear the adaptations.

Thanks!

Often overlooked with Lamda/O2 issues is cam position sensors.

After chasing with several primary, secondary O2 plus spark plug replacements, the cam position sensors install seemed to do remedy my issues...

smokinjoe64 wrote

Often overlooked with Lamda/O2 issues is cam position sensors.

After chasing with several primary, secondary O2 plus spark plug replacements, the cam position sensors install seemed to do remedy my issues...

What codes were you getting that replacing the cam position sensor resolved?


I installed the 2 new pre-cat O2 sensors yesterday as well as the thermostat and the coolant temp sensor. Unfortunately code 2725 is back. Clearing the codes with the engine off, it comes right back. I cleared it with the engine running and it stayed off until I started the car back up.

I guess I need to properly diagnose this with ISTA. I'm fairly certain this is a wiring issue as I mentioned in my first post, the previous owner had an O2 sensor wire harness repair listed in his service history. I'm having trouble finding much info on the 2725 code if anyone has any insight, I'm all ears.

Good news is the thermostat was definitely faulty, not sure about the temp sensor but with the new tstat and sensor in, I'm getting 181-185 on my water temp display (M Performance steering wheel v2) consistantly and it seems to warm up quicker. My gas mileage has improved as well.

darren p. wrote

What codes were you getting that replacing the cam position sensor resolved?


I installed the 2 new pre-cat O2 sensors yesterday as well as the thermostat and the coolant temp sensor. Unfortunately code 2725 is back. Clearing the codes with the engine off, it comes right back. I cleared it with the engine running and it stayed off until I started the car back up.

I guess I need to properly diagnose this with ISTA. I'm fairly certain this is a wiring issue as I mentioned in my first post, the previous owner had an O2 sensor wire harness repair listed in his service history. I'm having trouble finding much info on the 2725 code if anyone has any insight, I'm all ears.

Good news is the thermostat was definitely faulty, not sure about the temp sensor but with the new tstat and sensor in, I'm getting 181-185 on my water temp display (M Performance steering wheel v2) consistantly and it seems to warm up quicker. My gas mileage has improved as well.

darren p. since issues resolved early summer, didn't retain codes; however, these were the related code symptoms/descriptions from recall below.

• Mostly Bank 1 w/misfires [cyl 1] also bank 2 intermittently
• O2s - Fouled & changed 3x primaries; 2x rear
• Limp mode 2x
• Emissions codes [rich]
• Crank sensor failed
• Camshaft sensor - 1 of 2 turned out bad [did swap to verify][/INDENT]

Also posted on 'O2 sensor and Misfire' threads to .
One example post, referencing part changes along the way...good luck on the journey!

smokinjoe64 wrote

darren p. since issues resolved early summer, didn't retain codes; however, these were the related code symptoms/descriptions from recall below.

Lambda related:

• Mostly Bank 1 w/misfires [cyl 1] also bank 2 intermittently
• O2s - Fouled & changed 3x primaries; 2x rear
• Limp mode 2x
• Emissions codes [rich]
• Crank sensor failed
• Camshaft sensor - 1 of 2 turned out bad [did swap to verify][/INDENT]

Also posted on 'O2 sensor and Misfire' threads to .
One example post, referencing part changes along the way...good luck on the journey!

Thanks, I'm not having any misfire issues thankfully. No limp mode, no other codes now other than bank 2 2725...