1.5KVIEWS
7REPLIES
3APPRECIATES
07-13-2025LAST POST
2012 with 160k miles and starting to show her age.

I've been getting an intermittent Increased Emissions CEL that past few months. Light will go out and may not come back for a month or two, but the following codes continue to populate (via Carly):

2772 -O2 sensor pre cat bank 2

27AA -DME: Charge plausibility, diagnostic hot -bank 1

27AB -DME Charge plausibility, diagnostic hot -bank 2

Back In June I did have 2771 (O2 pre cat bank 1) pop up as well with the same codes as above, but it has not since then.

The only symptom is a slightly rough idle at times (rpms stay steady). The other morning with a cold start I did have some RPM fluctuations as I drove off in cooler temps and over the years this hasn't been that uncommon in colder weather. Normally I wait for the cold start cycle to complete but was in a rush.

Plugs, Fuel tank breather valve (2nd time), thermostat and sensor replaced back in late May or early June.

I'm going to guess bank 2 pre cat sensor, but in my search for the same codes came across the low pressure fuel sensor as a possible cause when getting both 2772 and 2771 codes.

Any help or guidance is much appreciated.
Thanks
-Nick

Update: 2 years later now with 196,000 miles, last summer, same codes intermittently in hotter weather, no CEL during the winter/fall/spring. This summer (which has been hotter and more humid than normal), again, CEL 27AA, 27BB and sometimes 2771. More consistently popping up. Last weekend I replaced both primary (pre-cat) O2 sensors with Bosch ones. 150 or so miles later, codes are back. I did replace one of the TA earlier this summer as well as spark plugs. The codes started popping up not that long after that, but the weather started getting warmer then. Any thoughts? Once more, slightly rough idle sometimes, seems to drive fine other wise.
you should've replaced all 4 o2 sensors together, they were available on rock auto with the bosch part number.
Update: 2 years later now with 196,000 miles, last summer, same codes intermittently in hotter weather, no CEL during the winter/fall/spring. This summer (which has been hotter and more humid than normal), again, CEL 27AA, 27BB and sometimes 2771. More consistently popping up. Last weekend I replaced both primary (pre-cat) O2 sensors with Bosch ones. 150 or so miles later, codes are back. I did replace one of the TA earlier this summer (due to failure) as well as spark plugs. The codes started popping up not that long after that, but the weather started getting much warmer then. Any thoughts? Once more, slightly rough idle sometimes, seems to drive fine other wise.

In summary, codes 27AA, 27ab, 2771 (in years past 2772). Primary o2 sensors changed, fuel pressure sensor changed. Slightly rough idle at times, otherwise seems to drive fine. Oil temps hotter than 5 years ago and prior, but has been that way the past 4 years (coolant, water pump, thermostat and sensor, oil thermostat/OFH all changed).
https://www.m3post.com/forums/showpost.php?p=15335672&postcount=37
https://www.m3post.com/forums/showpost.php?p=15335365&postcount=35

No mention of checking for intake leaks. Namely, your MAP sensor and associated "idle strip" components. An incorrect MAP reading from unmetered flow could cause this. A smoke test would be a worthy t/s step.

https://www.realoem.com/bmw/enUS/showparts?id=WD93-USA-12-2009-E92-BMW-M3&diagId=13_1241
RocketyMan wrote
https://www.m3post.com/forums/showpost.php?p=15335672&postcount=37
https://www.m3post.com/forums/showpost.php?p=15335365&postcount=35

No mention of checking for intake leaks. Namely, your MAP sensor and associated "idle strip" components. An incorrect MAP reading from unmetered flow could cause this. A smoke test would be a worthy t/s step.

https://www.realoem.com/bmw/enUS/showparts?id=WD93-USA-12-2009-E92-BMW-M3&diagId=13_1241
To check for intake leaks here, I imagine I would have to take the plenum off, otherwise you can't see anything. If so, would I just input the smoke at the ICV hose intake (the hose that attaches to the back underside of the plenum)?
nick3753 wrote
To check for intake leaks here, I imagine I would have to take the plenum off, otherwise you can't see anything. If so, would I just input the smoke at the ICV hose intake (the hose that attaches to the back underside of the plenum)?
Yes, you'll have to take off the plenum to gain access--not a big deal.
For a smoke test, you need to figure out a good location AFTER each throttle plate. I agree, I think a good location for smoke input would be the ICV hose intake. Then look at where your leaks are.

Investigate your MAP sensor and see whats going on there.

Report back your findings.
I am also dealing with an intermittent 2771 and sometimes 2772 when the weather gets hotter here. No noticeable drivability issues and never had a SES light.

I have in the past year replaced all 4 oxygen sensors when I replaced my x-pipe, so very unlikely that this is a sensor issue especially since I'm sometimes seeing both banks affected at the same time. I have run the o2 sensor diagnosis through ISTA a few times when I have seen the codes and each time it reports back that the sensors are normal in terms of their diagnosis setpoint.

Hoping to find some time when the car has completely cooled off to smoke test @ the ICV hose.
Attached imageAttached image
RocketyMan wrote
Yes, you'll have to take off the plenum to gain access--not a big deal.
For a smoke test, you need to figure out a good location AFTER each throttle plate. I agree, I think a good location for smoke input would be the ICV hose intake. Then look at where your leaks are.

Investigate your MAP sensor and see whats going on there.

Report back your findings.
Thank you for the advice. I should have snagged a smoke machine on Prime day. I will be traveling the next few weeks and preparing to sell my house in between, so I likely won’t get around to doing anything for a while. I’ll post back when I get to it.