Is your 2009 BMW 3 Series key fob acting up, especially when the temperatures drop? Many owners of the E90 3 Series experience issues with their key fobs in cold weather, noticing symptoms like reduced range for locking and unlocking, or the car starting without recognizing personalized settings such as radio presets. This is often due to a failing battery in your key fob. Fortunately, replacing the battery is a straightforward DIY task that can save you a trip to the dealership and the associated costs. This guide will walk you through the process of replacing your 2009 BMW 3 Series key fob battery.
Before you begin, it’s crucial to source the correct replacement battery. The BMW E90 key fob uses a VL2020 lithium-ion rechargeable battery. When purchasing, pay close attention to the battery terminals’ orientation, as they are offset at approximately 90 degrees. You can find the correct battery online; a suitable replacement option is available at this eBay link. Ensure the battery you purchase matches the VL2020 specification to guarantee compatibility and performance.
The key fob casing is securely glued, requiring careful opening. Use a sharp X-acto knife and gently score along the seam of the fob. Take your time and avoid applying too much pressure to prevent damage to the internal circuit board (PCB). Work your way around the entire perimeter of the key fob until you can begin to pry it open.
Once you have carefully separated the two halves of the key fob casing, you’ll need to desolder the old battery. To avoid accidental short circuits, use a non-metallic pry tool. A credit card or a plastic spudger works well. Gently apply a small amount of pressure under the battery at the corner terminal. Then, using a soldering iron, desolder the corner terminal first. This is important because the middle terminal’s lead is longer, and removing the corner terminal first provides space to maneuver.
With the old battery removed, position the new VL2020 battery into the battery holes on the PCB. Hold the PCB firmly by the edges and gently press the new battery down into place. Apply heat with your soldering iron to the middle terminal first, allowing the solder to flow and secure the battery. Repeat this process for the corner terminal. The battery terminals should push through the existing solder and seat correctly.
Before permanently sealing the key fob, perform a test. Dry fit the PCB back into the housing and test the key fob’s functions on your 2009 BMW 3 Series. Check if the lock and unlock buttons work and start your car to confirm the personalized settings are restored. If everything is functioning correctly, you’ve successfully replaced your BMW key fob battery.
Finally, you can reassemble the key fob. You have the option to purchase a new key fob housing for a pristine look. Alternatively, you can simply glue the original housing back together. If you choose to glue it, use a gel-type cyanoacrylate glue sparingly. Gel glue is less likely to run and minimizes the risk of accidentally gluing the PCB to the housing. Apply a small amount of glue to the edges of the casing and press the two halves together firmly until the glue sets.
By following these steps, you can effectively replace your 2009 BMW 3 Series key fob battery and resolve common issues related to cold weather or aging batteries. This DIY repair is a cost-effective solution that restores your key fob’s functionality and ensures you can reliably access and start your BMW.
