The diagnostic process starts by verifying that all tires are the correct and matching size, as mismatched tires can cause drivetrain binding. If tire sizes are correct, the next step is to use a scan tool to temporarily disable the all-wheel-drive system and test drive the vehicle. If the shuddering disappears, the issue is confirmed to be related to the transfer case.

The recommended repair is simply draining and replacing the transfer case fluid with the correct BMW-approved fluid. This commonly resolves the issue. In this case, the vehicle had only 35,000 miles, and once the fluid was replaced and the system reset, the shuddering was completely eliminated.

The transcript emphasizes not to misdiagnose the problem as an engine misfire and avoid unnecessary repairs such as replacing spark plugs, ignition coils, the transmission, or the transfer case. The fix is straightforward and effective when following BMW’s service bulletin.