Is your 2007 BMW 335i key fob acting up, especially when the temperature drops? You’re not alone. Many BMW owners experience issues with their key fobs in cold weather, ranging from difficulty locking and unlocking doors to the car failing to remember personalized settings. Often, the culprit is a dying key fob battery. Instead of heading straight to the dealership and facing potentially high costs, you can easily tackle a 2007 Bmw 335i Key Fob Battery Replacement yourself. This guide will walk you through the process step-by-step.
Before we begin, let’s understand why this happens. BMW key fobs for models like the 2007 335i use a rechargeable lithium-ion battery (VL2020). Over time, like any battery, this will degrade and hold less charge. Cold temperatures exacerbate this issue, reducing battery performance and leading to the problems you might be experiencing. Symptoms of a low key fob battery in your 2007 BMW 335i can include:
- Reduced Range: You need to be closer to your car for the key fob to work.
- Intermittent Functionality: The key fob works sometimes but not others, especially in cold weather.
- Settings Reset: Your BMW may not remember your personalized settings like radio presets or seat positions after starting the car.
- “Comfort Access” Issues: If your BMW is equipped with comfort access, you might find it’s less reliable or stops working altogether.
Replacing the battery is a straightforward DIY task that can save you time and money. Here’s how to do it:
What You’ll Need:
- Replacement Battery: A VL2020 lithium-ion rechargeable battery. Ensure you purchase the correct type with the terminals oriented at approximately a 90-degree offset. You can find these online from reputable sellers.
- Precision Knife (X-acto knife or similar): A sharp knife is crucial for carefully opening the glued key fob.
- Soldering Iron and Solder: You’ll need basic soldering skills to remove the old battery and install the new one.
- Non-Metallic Pry Tool (Credit Card or Plastic Spudger): For gently prying the battery without causing a short circuit.
- Glue (Cyanoacrylate gel type recommended): To re-seal the key fob casing.
Step-by-Step 2007 BMW 335i Key Fob Battery Replacement:
Step 1: Carefully Open the Key Fob Casing
The BMW key fob is sealed with glue, requiring a careful approach to open it without damaging the internal components. Using your sharp X-acto knife, gently score along the seam line of the key fob. It’s crucial to avoid cutting too deep to prevent damage to the circuit board (PCB) inside. Work slowly and patiently, going around the entire perimeter of the fob multiple times, gradually deepening your cut until the case begins to separate.
Step 2: Desolder the Old Battery
Once the key fob is open, you’ll see the PCB with the battery soldered in place. To remove the old battery, you’ll need to desolder it. The original guide suggests using a non-metallic pry tool to apply slight tension to the battery. A credit card or a plastic spudger works well for this, reducing the risk of short-circuiting anything. Focus on desoldering the corner terminal first. This is because the middle terminal has a longer lead, making it harder to get under the battery to apply tension initially. Heat the solder joint of the corner terminal with your soldering iron and gently pry upwards on the battery with your non-metallic tool until the solder melts and the terminal releases. Repeat this process for the remaining terminal(s).
Step 3: Solder in the New VL2020 Battery
Now, position the new VL2020 battery into the battery holes on the PCB. Hold the PCB from the edges and apply gentle pressure downwards onto the battery to ensure the terminals are correctly seated. Apply heat to the middle terminal first, then the corner terminal, allowing the battery terminals to push through the existing solder and settle into place. Ensure a good solder joint for a reliable connection.
Step 4: Test and Reassemble
Before permanently sealing the key fob, it’s crucial to test if the new battery is working correctly. Dry fit the PCB back into the key fob housing and test all the key fob functions – locking, unlocking, remote start (if applicable), and comfort access. If everything works as expected, congratulations! You’ve successfully completed your 2007 BMW 335i key fob battery replacement.
For reassembly, you have a couple of options. You can purchase a new key fob housing for a fresh look, or simply glue the original housing back together. If you choose to glue it, use a gel-type cyanoacrylate glue sparingly. The gel consistency prevents it from running and potentially gluing the PCB to the housing. Apply a small amount along the seam and carefully press the two halves of the key fob together until the glue sets.
Conclusion
Replacing the battery in your 2007 BMW 335i key fob is a manageable DIY project that can resolve common key fob issues, especially those arising in cold weather. By following these steps, you can restore your key fob’s functionality and avoid unnecessary dealership expenses. Remember to take your time, be careful when opening the fob and soldering, and always test before finalizing the reassembly. Enjoy the reliable performance of your key fob once again!
