BMW E90 diesel: mass air flow sensor (MAF) and fault code 3FF0
What does fault code 3FF0 mean on a BMW E90 diesel?
Code 3FF0 means that the air quantity measured by the mass air flow sensor (MAF) is too high compared with what was requested. The cause is not always the sensor. Common causes include an air leak on the boost side, for example a faulty seal on the intercooler hose, or the EGR system's vacuum valve.
Does an adaptation have to be done after replacing the mass air flow sensor?
Opinions vary. According to the instructions, the adaptation is done after replacement and the old correction values are reset with a diagnostic tool. On the other hand, the control unit is said to learn the new sensor's values while driving. Doing the reset does not change the engine program.
When does the mass air flow reading point to a fault other than the sensor?
The MAF value of a running engine is never 0 g/s. If at idle the reading swings back and forth by more than 10 g/s, the fault is more likely elsewhere than in the sensor itself, for example in the wiring.
Can a faulty mass air flow sensor raise consumption?
It can. Replacing the sensor has clearly lowered the consumption shown by the on-board computer. The cause of poor efficiency can still be something else, for example a clogged particulate filter, so you should not rely on replacing the sensor alone before measuring.