Why the same message covers different problems
Our repair pages list "drivetrain malfunction" as a symptom of several unrelated failures. That is why a scan for the actual fault codes matters more than the message itself. The sections below group the causes by what else the car is doing: stalling or loss of power, a boost loss with a pop, shudder on tight turns, or a rattle from the front of the engine. The pages are reported repairs, not a ranking of likelihood.
Fuel: the in-tank low pressure pump
On the F30, F32, F22, F10 and B46 and B48 cars, the in-tank pump is listed with a drivetrain malfunction warning and loss of power, stalling often at low fuel, a long crank before start and an inaccurate fuel gauge. The pump is reached under the rear seat with no tank drop, and owners report 30 to 45 minutes for the swap. Confirm whether the fault is the pump, its built-in level sensor or the tank sensor before replacing parts, and note that California and other CARB-state cars may be covered by the emissions warranty. See Low Pressure Fuel Pump (In-Tank).
Boost: charge pipe and turbo
A loud pop followed by a sudden loss of boost, with limp mode or a drivetrain malfunction message and a hiss under acceleration, is the cracked plastic charge pipe on the N55 and N20. Most commenters recommend an aluminum aftermarket pipe so it does not crack again. See N55 Charge Pipe.
On the N20 and N26, the turbo page lists drivetrain malfunction alongside wastegate rattle, boost control faults, blue smoke on cold start and loss of power under boost. Labor is often quoted at 8 to 10 hours, and blue smoke on cold start is sometimes only the updated oil feed line. See N20 / N26 Turbocharger Replacement.
xDrive: transfer case actuator and fluid
On F and G-chassis xDrive cars, a drivetrain malfunction warning with shudder or binding on tight turns, xDrive stuck in rear-wheel drive or whining near the center of the car points at the transfer case actuator. Dealers sometimes quote a full transfer case when only the actuator is bad, so diagnose before paying, and ISTA programming is usually required. Uneven tires accelerate wear. See Transfer Case Actuator (xDrive VTG).
The transfer case fluid page lists drivetrain malfunction after neglected fluid, and notes the wrong fluid causes shudder. See Transfer Case Fluid (xDrive).
The expensive one: timing chain on the N63
On the N63 V8, a rattle on cold start from the front of the engine, timing or camshaft position codes and plastic guide pieces in the oil pan come before a jumped chain, which brings a drivetrain malfunction message and a whole bank misfiring. Ask BMW about goodwill, because one owner got 75 percent covered. See N63 V8 Timing Chains & Guides. The N20 timing chain page lists a similar rattle and whine (N20 Timing Chain & Guides), and the BMW Cold Start Rattle, Whine and Squeal: Causes by Engine sorts engine noises by sound. For shudder and shake, see the BMW Vibration and Steering Shimmy: Brakes, Mounts and Driveshaft.