how to diagnose a burning smell from my BMW 3 Series E90/E91 (2005-2012) transmission?

Solution

1. Preparation

• Tools Required: Socket set, OBD-II scanner, transmission fluid pump, drain pan.
• Safety Warnings: Allow the engine to cool before working on the transmission. Ensure the vehicle is on a level surface and securely supported.

2. Replace Transmission Fluid

1. Drain Old Fluid:
   • Place a drain pan under the transmission pan.
   • Remove the transmission pan bolts and carefully lower the pan to drain the fluid.
2. Inspect and Clean Pan:
   • Clean the transmission pan and remove any debris or sludge. Inspect the pan for damage.
3. Replace Filter (if applicable):
   • Remove the old filter and install a new transmission filter. Ensure it is seated properly.
4. Reinstall Pan:
   • Reinstall the transmission pan with a new gasket (if required) and torque the bolts to manufacturer specifications.
5. Add New Fluid:
   • Use a transmission fluid pump to add new, manufacturer-recommended transmission fluid through the fill port.
   • Check the fluid level with the dipstick and adjust as necessary.

3. Inspect Transmission Components

1. Check for Internal Damage:
   • If the burning smell persists, further disassembly may be required to inspect internal components such as clutches and bands for wear or damage.
   • Replace any damaged components as necessary.