why does my BMW 3 Series G20/G21 (2019-2024) transmission slip when shifting gears?

Solution

1. Preparation

• Tools Required: OBD-II scanner, socket set, multimeter, transmission fluid pump, fluid catch pan.
• Ensure the vehicle is on a level surface and the engine is turned off.
• Disconnect the battery to prevent electrical shorts.

2. Fluid Inspection and Replacement

• Sub-steps:
  1. Remove the transmission fluid fill plug using a socket.
  2. Check fluid level; if it is low, proceed to drain and replace.
  3. Place the fluid catch pan under the transmission pan and remove the drain plug.
  4. Allow the old fluid to completely drain out.
  5. Replace the drain plug with a new gasket and torque to manufacturer specifications.
  6. Use the transmission fluid pump to fill the transmission with the correct type of new fluid (refer to owner's manual for specifications).
  7. Replace the fill plug and ensure it is properly torqued.

3. Electrical and Software Check

• Sub-steps:
  1. Reconnect the battery.
  2. Use the OBD-II scanner to check for any software updates needed for the TCM.
  3. If updates are available, follow the manufacturer’s instructions to apply them.
  4. Inspect and repair any damaged wiring or connectors to the transmission.

4. Test Drive

• Sub-steps:
  1. Start the vehicle and allow it to reach operating temperature.
  2. Perform a test drive to monitor transmission performance.
  3. Observe shifts and check for any slipping; if resolved, proceed to verification.