What does BMW 4x4 malfunction mean?

[JohnLynn]

BMW 4x4 malfunction refers to the central differential failure. BMW four-wheel drive principle: The central differential understands the vehicle's condition based on information received from sensors, then distributes power transmission between the front and rear axles to achieve four-wheel drive. Function of the central differential: In multi-axle drive vehicles, the drive axles are connected by drive shafts. To allow different input angular speeds between drive axles and eliminate wheel slippage, a central differential (also called inter-axle differential) can be installed between the drive axles. When the vehicle turns, the curve distances covered by the inner and outer wheels are obviously different in the same time period - the outer wheels travel farther than the inner wheels. If both wheels are fixed to the same rigid rotating shaft with equal angular velocity, the outer wheel must experience rolling slip while the inner wheel must experience rolling skid.