how to fix BMW 3 Series E90/E91 (2005-2012) transmission fluid leak

Solution

1. Preparation

• Tools Required: Socket set, torque wrench, fluid pump, drain pan, rags.
• Raise the vehicle securely using jack stands.
• Allow the engine to cool completely before starting work.

2. Drain Transmission Fluid

• Place a drain pan under the transmission pan.
• Remove the transmission pan bolts using the socket set and gently pry the pan off.
• Allow the old fluid to drain completely into the pan.

3. Inspect and Replace Gaskets/Seals

• Remove the old transmission pan gasket and inspect for wear or damage.
• If the leak is from the transmission cooler lines, replace the seals or the entire line as needed.
• For output/input shaft seals, remove the old seals using a seal puller and install new seals.

4. Clean and Reinstall Transmission Pan

• Clean the transmission pan thoroughly and remove any old gasket material from the mating surface.
• Apply a new gasket or RTV sealant as per manufacturer specifications.
• Reinstall the transmission pan and torque the bolts to the manufacturer’s specifications (usually around 10-12 Nm, but check service manual for exact values).

5. Refill Transmission Fluid

• Use a fluid pump to fill the transmission with the correct type of fluid as specified in the owner’s manual (typically, BMW uses ATF fluid).
• Start the engine and allow it to reach operating temperature, then check the fluid level again, adding more fluid as necessary.