# Mass airflow sensor failure related to CBU?



## 3ismagic# (Mar 17, 2011)

So I went in and had my SES light checked. They diagnosed a faulty mass air flow sensor and replaced it.

Any chance this is indicative of CBU issues in the near future?


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## montr (Oct 7, 2006)

It is a sign, not definitive but a possibility. CBU introduce an air mass deviation. See attachments.

You could have CBU buildup and they mis-diagnosed it and replaced a good part.


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## 3ismagic# (Mar 17, 2011)

Here is what it said specifically:

Effective Mass air flow sensor. Implausible intake air temp sensor.
inspected and road tested. scoped vehicle and found faults for mass air flow. followed test plan and found intake air compare to charge air is not ok. checked charge air sensor and found ok. checked intake air temp sensor and found out of spec. replaced mass air flow sensor and performed adaptation. cleared faults and road tested. no faults returned.


part number 13-62-8-509-725 hot-cil air mass


thoughts.

FYI My car is a july 2011 build (one of the last 335ds) with 27k miles.


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## Hoooper (Jun 17, 2013)

3ismagic# said:


> FYI My car is a july 2011 build (one of the last 335ds) with 27k miles.


wow. Lots of short trips, or just rarely driven? MAF errors can be indicative of CBU, but they do just fail on their own as well


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## 3ismagic# (Mar 17, 2011)

Mostly short trips. 8 months after we bought we moved cross country from a big city to a small college town. My commute and pretty much anything I ever drive to is less than 15 minutes. with occasional 400-500 mile road trip.

around town I've mostly tried to drive in sport mode, but who knows if that has really helped. My warranty expires in a few days. Hopefully in I get the CBU in the next several months I can convince them to fix it for free seeing as it has such low miles.


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## Thisonegoesto11 (Apr 22, 2015)

I had the MAF sensor start acting up on mine recently. Did a smoke test and found one of my hoses had been broken and replaced by someone with some USA tubing. It was obviously not making a full seal. Replacing the part now. I had CBU cleaning done at 100k miles. At 119k right now. I was getting similar codes to you. If the codes come back, maybe do a smoke test to look for a leak.


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## totitan (May 11, 2013)

3ismagic# said:


> Mostly short trips. 8 months after we bought we moved cross country from a big city to a small college town. My commute and pretty much anything I ever drive to is less than 15 minutes. with occasional 400-500 mile road trip.
> 
> around town I've mostly tried to drive in sport mode, but who knows if that has really helped. My warranty expires in a few days. Hopefully in I get the CBU in the next several months I can convince them to fix it for free seeing as it has such low miles.


Short trips are the kiss of death for these cars. I bought mine with 34,000 miles a little over two years ago and now its at 81,000 without issues. For short trips around town we use the VW.


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## Thisonegoesto11 (Apr 22, 2015)

Thisonegoesto11 said:


> I had the MAF sensor start acting up on mine recently. Did a smoke test and found one of my hoses had been broken and replaced by someone with some USA tubing. It was obviously not making a full seal. Replacing the part now. I had CBU cleaning done at 100k miles. At 119k right now. I was getting similar codes to you. If the codes come back, maybe do a smoke test to look for a leak.


Unfortunately I still had to replace the MAF sensor. It was going bonkers after I got the vacuum seal addressed. Quick plug and play with the sensor. The car runs like a champ now. So I guess these MAF sensors are something to watch out for.


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## pasing (May 11, 2011)

This was the code I got (as I previously posted) on my 2011 with 37k miles last month when my SES came on:

P0101. Mass or Volume Air Flow A
Circuit Range / Performance

Not sure if this is the same thing as the MAF. Turned out to be CBU.


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## 335duff (Jul 30, 2015)

My car had its first one replaced around 25k and the second around 39k.

No CBU diagnosed yet.


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## n1das (Jul 22, 2013)

Thisonegoesto11 said:


> Unfortunately I still had to replace the MAF sensor. It was going bonkers after I got the vacuum seal addressed. Quick plug and play with the sensor. The car runs like a champ now. So I guess these MAF sensors are something to watch out for.


I just had the MAF sensor replaced along with an EGT sensor and boost pressure sensor in my 2012 X5 35d. The open O2 sensor recall was also taken care of. Everything was covered under CPO warranty. There were no air leaks (smoke tested) but 3 sensors mysteriously threw codes all at the same time.

It's strange that 3 sensors would suddenly fail all at the same time. There were codes thrown for all 3 sensors plus other codes that might be triggered due to these faults. It puked a long list of codes and went in to limp mode. Fortunately I was only a few miles from home and my BMW dealer is only 3 miles away from home.

All 3 sensors had to be replaced to clear all codes. Car runs like a champ and actually runs BETTER than it did before it started acting up over the past weekend. I suspect the MAF was slowly fading and the drop in power was so gradual over time and miles that I didn't notice it. The EGT sensor might have already been dead for a while. The car has never lacked power and this is the first time it has ever thrown a code and acted up. Power is now better than before and mileage seems to be slightly improved.

The X5 35d was built in early 2012 and bought used in 2014 (CPO deal) at 52k miles. The original owner did mostly highway driving and traded it in and basically threw a perfectly good car away as soon as the original factory warranty was done and free service ended. The car now has 96k miles on it. It has never been babied and always driven hard on the highway like it was stolen and for long periods. Given how well it's running with my heavy right foot all the time I don't think CBU is a problem.


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## Wannabe32 (Jul 2, 2014)

*MAF, CBU or both?*

Sorry for posting to an older thread.

2011 335d with 58k and just got the SES light. Great news.
Codes are P0101 only.
Car seems to still run well and haven't noticed any decline is gas mileage which has been around 33.6 for a very long time.

Before taking it in I was hoping to get some input on whether a new Mass Air Flow sensor is likely to fix this or if I should start budgeting and calling around for a carbon cleaning. Seems like a waste to do both.

Not happy but sounds like I'm not alone.


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## Nadir Point (Dec 6, 2013)

Wannabe32 said:


> ...gas mileage which has been around 33.6 for a very long time.


How long since the MPG calculation was reset?


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## Wannabe32 (Jul 2, 2014)

Nadir Point said:


> How long since the MPG calculation was reset?


It had been awhile. I reset it on the way home and it drifted down to about the same.


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## Nadir Point (Dec 6, 2013)

Then I wouldn't suspect CBU if it's still pulling >30MPG in any form of mixed driving.


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## n1das (Jul 22, 2013)

Wannabe32 said:


> Sorry for posting to an older thread.
> 
> 2011 335d with 58k and just got the SES light. Great news.
> Codes are P0101 only.
> ...


Your GAS mileage is technically infinite at all times due to zero gasoline used. 

Sent from my Nexus 6 using Tapatalk


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## Wannabe32 (Jul 2, 2014)

n1das said:


> Your GAS mileage is technically infinite at all times due to zero gasoline used.
> 
> Sent from my Nexus 6 using Tapatalk


My wife corrects me on that all the time when I go to fill up. Thanks for the reminder.


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