Possible reasons for automatic transmission jerking when changing gears in BMW cars:
Mechanical:
* Worn or damaged friction discs
* Worn or dirty solenoids
* Faulty torque converter
*Low or contaminated transmission fluid
* Worn or damaged gears
* Servo problems
Electronic:
* Faulty speed sensor
*Faulty throttle position sensor
* Problems with the automatic transmission electronic control unit (ECU)
Other:
* Worn or damaged engine or transmission mounts
*Low fuel pressure
* Problems with electrical harness
* Irregularities in the automatic transmission software
Stages of diagnostics and troubleshooting:
1. Checking the level and condition of the transmission fluid: Check the fluid level and visually assess its color and smell. Dirty or cloudy fluid may indicate wear or damage to the automatic transmission.
2. Inspect the solenoids and friction discs: Remove the transmission pan and inspect the solenoids and friction discs for wear or damage.
3. Scan with a diagnostic scanner: Connect the diagnostic scanner to the vehicle and read the trouble codes. The codes may indicate faulty sensors, ECU problems, or other electrical problems.
4. Checking transmission fluid pressure: Use a pressure gauge to measure fluid pressure at various points in the automatic transmission. Low pressure may indicate a worn pump or a leak in the system.
5. Inspection of Gears and Other Mechanical Components: Remove the automatic transmission from the vehicle and inspect the gears, shafts and other mechanical components for wear or damage.
It is recommended to contact a qualified service center for diagnosis and repair of the automatic transmission.