Mass airflow, Intake air temp fault

friedymeister · 04-20-2021, 09:34 PM

Hi everyone,

My 2011 135 convertible 6MT started throwing some codes in the last week. After startup, I had a rough idle for a minute or two with a CEL and a bunch of codes. I had a misfire code for each cylinder, 29D0 "intake air temp sensor, electrical, short circuit to B+." 277A "air-mass flow sensor , signal: electrical fault."

I cleared the codes, turned it on again and had no idle issues and no misfire codes, but the CEL came back on with the same 29D0 "intake air temp sensor, electrical, short circuit to B+." 277A "air-mass flow sensor , signal: electrical fault."

My car has never been modified and is completely stock 6MT. Does anyone have any idea what is going on?

Thanks in advance!

MightyMouseTech · 04-21-2021, 02:39 PM

Check the wiring going to the MAF.

friedymeister · 05-25-2021, 08:58 AM

Quote:

Originally Posted by MightyMouseTech

Check the wiring going to the MAF.

That was great advice- I got everything ready to clean my MAF when I found this under the hood.

It looks like the harness was severed and I don't see where it connects. Does anyone know how to go about replacing this?

tracer bullet · 05-25-2021, 09:31 AM

The other end would have to be nearby, just have to look for it. Then see how far you can trace it back.

Might have to remove the cowling, but it isn't bad, look up a spark plug DIY and it'll have the details for that. Could help you get even further before something disappears.

The "realoem" site has great parts drawings, and might give you a clue how long this wire goes, if it's fairly short to get to another plug or if it's bundled w/ a major grouping of them.

Strip, twist, solder, shrink wrap (wrap put in place before twist and solder!) could connect them. If I remember right there's some free play in that one so it can be reconnected without hugely stretching it afterwards.

I'd also see what cut it to start with. It's in the neighborhood of where the hood closes and is a logical thing that might have done it, but I'm kind of finding that hard to believe. After it's repaired at least be sure to look into that so it doesn't happen again.

friedymeister · 05-25-2021, 09:53 AM

Thank you!

The way it's cut like that I wonder if it was a rodent.

MightyMouseTech · 05-27-2021, 04:50 PM

Quote:

Originally Posted by friedymeister

Thank you!

The way it's cut like that I wonder if it was a rodent.

That 100% looks like rodent damage.

Glad you found the issue.

04-20-2021, 09:34 PM	#1
friedymeister Private 5 Rep 73 Posts Drives: 2011 BMW 135i Convertible Join Date: Jul 2009 Location: Westchester NY iTrader: (0)	Mass airflow, Intake air temp fault Hi everyone, My 2011 135 convertible 6MT started throwing some codes in the last week. After startup, I had a rough idle for a minute or two with a CEL and a bunch of codes. I had a misfire code for each cylinder, 29D0 "intake air temp sensor, electrical, short circuit to B+." 277A "air-mass flow sensor , signal: electrical fault." I cleared the codes, turned it on again and had no idle issues and no misfire codes, but the CEL came back on with the same 29D0 "intake air temp sensor, electrical, short circuit to B+." 277A "air-mass flow sensor , signal: electrical fault." My car has never been modified and is completely stock 6MT. Does anyone have any idea what is going on? Thanks in advance!
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04-21-2021, 02:39 PM	#2
MightyMouseTech Major General 4393 Rep 6,202 Posts Drives: 13 135i 6MT LeMans Blue MSport Join Date: Feb 2013 Location: Ottawa, Canada iTrader: (0)	Check the wiring going to the MAF.
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05-25-2021, 09:31 AM	#4
tracer bullet Major General 6189 Rep 6,188 Posts Drives: '25 Z4, '15 X3 35i (135i sold) Join Date: May 2011 Location: Saint Paul, MN iTrader: (1)	The other end would have to be nearby, just have to look for it. Then see how far you can trace it back. Might have to remove the cowling, but it isn't bad, look up a spark plug DIY and it'll have the details for that. Could help you get even further before something disappears. The "realoem" site has great parts drawings, and might give you a clue how long this wire goes, if it's fairly short to get to another plug or if it's bundled w/ a major grouping of them. Strip, twist, solder, shrink wrap (wrap put in place before twist and solder!) could connect them. If I remember right there's some free play in that one so it can be reconnected without hugely stretching it afterwards. I'd also see what cut it to start with. It's in the neighborhood of where the hood closes and is a logical thing that might have done it, but I'm kind of finding that hard to believe. After it's repaired at least be sure to look into that so it doesn't happen again.
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05-25-2021, 09:53 AM	#5
friedymeister Private 5 Rep 73 Posts Drives: 2011 BMW 135i Convertible Join Date: Jul 2009 Location: Westchester NY iTrader: (0)	Thank you! The way it's cut like that I wonder if it was a rodent.
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