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      12-12-2018, 01:31 AM   #1
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ELP! E90 Acceleration Hesitation with High Aux Fan? (MAF/IAT Codes)

Car: 2011 328i xDrive SULEV (N51), Manual Trans (6 speed)

Issue: Last week I noticed when shifting from 4th to 5th and 5th to 6th my car would hesitate before accelerating. Even at WOT, I would receive no power for 2-3 seconds. This was weird but it only happened a couple of times. Then a couple days later (this past weekend), this hesitation happened in between every gear and has continued to happen. Also, when heel/toe'ing to downshift there is no response from the throttle.
Later that day, when I turned on my car the aux fan started running on high (outside temp is 25-35deg F) and would stay on continually while driving, in addition to the hesitation.

Doing some searching, the aux fan condition seems to be a sign of an impending water pump failure. Apparently there should be some codes thrown when this happens, before the check engine light comes on.

So I decided to do the sensible thing and buy a bluetooth scanner - so I bought a "Carista" and used the 1 month of free full features to get BMW-specific codes.

Yesterday: Codes for IAT Circuit High Input (P0113) and MAF Circuit Problem (P0100) appeared, but no water pump codes. So I ordered a new MAF/IAT sensor. Issues continue with hesitation and high aux fan.
Today: (The sensor has not arrived yet) I check for codes again but the IAT and MAF codes do not appear! Issues still continue with hesitation and high aux fan.

A few questions:
1. Is this Carista crap and should I return it and get a more reliable scanner?
2. This sounds like an MAF issue to me - what does the bimmerforum universe think? Would my check engine light appear if my MAF failed (because it has not)?
3. If my MAF/IAT failed, could it lead to my aux fan running on high, or are these separate issues?

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      12-16-2018, 10:51 AM   #2
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I'm thinking MAF and IAT are not related to engine cooling and they are separate issues. IAT handles only cabin heating / cooling if i'm not mistaken and MAF just controls air / fuel ratios? If you unplug the MAF it will throw a code eventually. I think it is possible to "code" the MAF out so it can run without but that is someone else's specialty.

You're right about the codes bring thrown before water pump failure but they are shadow codes with no check engine light.

Also the P000 codes are generic OBD2 and not bmw specific, a $5 bluetooth adapter could read those. BMW codes are 4 number / letter combos and require other ways of reading. I personally am using that bimmer geeks app on my phone but I would recommend the tried and true way through INPA and a spare laptop if you're somewhat knowledgeable about those things.

It's worth doing research and properly diagnosing before committing to buying things for these cars or you might be throwing away money on things that may not be broken or failing. I'm guilty of that myself often times. I think I'll have a new car by the time I'm done.
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      02-22-2019, 05:46 AM   #3
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MAF and IAT sensor are inside the same sensor. IAT is Intake Air Temperature.

It is common for those two to appear if the sensor was left disconnected and the engine started/run after removing the airbox for example.
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aux fan, carista, codes, faults, iat, maf, sensor

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