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BMW 3-Series and 4-Series Forum (F30 / F32) | F30POST > Technical Forums > N47 and N57 Turbodiesel Engine / Drivetrain / Exhaust Modifications > Mass airflow sensor spontaneously disconnecting
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      10-07-2015, 12:31 PM   #1
Clearmysix
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Mass airflow sensor spontaneously disconnecting

Hello All,

I have a 2014 328d with 20k miles on it. It has done fairly well without major issues.

However, about 4 weeks ago I was suddenly accelerating from about 10mph and the car made some very loud, rough engine noises which prompted me to let off the gas. No engine warning lights at that time and the car continued to drive normally.

About 4 hours later I tried again to accelerate quickly and it did the same thing - then the engine fault came on, and instructed me me drive conservatively.

I took it to the dealer and they said that I had simply unplugged the mass air flow sensor, they plugged it in, said the car was now functioning normally, and it would cost me 165 dollars (since they said I had caused the problem).

I never touched the engine before so I complained and they later waived the fee.


One week later, same problem with acceleration, same engine code.

I took it back to the dealer, thinking that there must be a much larger problem going on, and they have just called me telling me I have again unplugged my mass air flow sensor and they asked me if I was attempting to mod the car.

I told them that this appears to be happening spontaneously (but they say its impossible).


Anyone have any experience like this? Very odd.
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      10-07-2015, 05:44 PM   #2
M-terkait
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maybe it's time for them to give you a loaner and test the car?
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      10-07-2015, 07:35 PM   #3
Clearmysix
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I have a loaner. They have now had my car for 2 separate weeks.
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      10-14-2015, 11:52 AM   #4
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If the sensor is plugged in correctly (clip engaged and snugly inserted) there really is no way for it to "come unplugged". If there were some issue with the harness being tight or caught on something and the hard acceleration caused the engine to flex on the mounts enough to supply tension.......it could only pull it loose if the plug was not inserted fully or if it snapped the clip.

Assuming the dealer would have mentioned a damaged clip, so either you have a gremlin who is unplugging it to mess with you, or.......well......
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      10-15-2015, 06:53 PM   #5
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So my car is now fixed. Apparently a motor mount was broken which under load would torque the engine into a position where it would disconnect the mass air flow sensor.

New motor mount and no more issues.

They did say that the mass air flow clip was functioning perfectly.
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      10-15-2015, 07:01 PM   #6
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Good guess thumper.
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