Is your 2003 BMW 325xi key fob acting up? Do you have to press the buttons multiple times, or get extremely close to your car for it to respond? You’re likely facing a common issue: a dead or dying key fob battery. While some might believe the urban legend that BMW key fob batteries recharge while driving, this isn’t the case for the 2003 325xi and similar models. The good news is, replacing the battery yourself is a straightforward process that can save you a trip to the dealership and unnecessary expense.
This guide will walk you through each step of replacing the battery in your 2003 BMW 325xi key fob. No need to worry about complicated procedures – with a few simple tools and a little patience, you can restore your key fob to perfect working order.
Tools and Materials You’ll Need
Before you begin, gather these essential tools and materials:
- Replacement Battery: Panasonic VL2020 with tabs (or a standard VL2020 battery and solder if you prefer to attach your own leads).
- Small Flathead Screwdriver or Paint Scraper: For prying open the key fob case.
- Sharp Knife or Utility Knife: To carefully cut along the glued seam of the fob.
- Vice-Grips or Pliers: To hold the key securely while opening.
- Soldering Iron with Fine Tip: For desoldering the old battery and soldering in the new one.
- Silver Solder: For making secure electrical connections.
- Small Chisel or Pocketknife: To remove the old battery leads.
- Wide Jaw Pliers (Channel-Locks) and Rubber Band: To hold the circuit board steady during soldering.
- Plastic Glue: To re-seal the key fob case.
- Clamps or Rubber Bands: To hold the case closed while the glue dries.
Step-by-Step Battery Replacement Guide
Let’s get started with the battery replacement process:
1. Opening the Key Fob Case
The BMW 325xi key fob case is notoriously glued shut, so opening it requires careful and deliberate action.
- Secure the Key: Use vice-grips to firmly hold the metal key part of the fob. This will give you leverage and prevent damage to the key itself.
- Start Prying: Begin at the key ring end of the fob. Insert the paint scraper or flathead screwdriver into the seam where the two halves of the case meet.
- Slice and Pry: Carefully use the sharp knife to slice along the glued seam while simultaneously gently prying with the scraper. Work your way around the perimeter of the fob, gradually cracking the case open. Be patient and avoid using excessive force, which could damage the internal components.
2. Identifying the Battery
Once the case is open, you’ll see the internal components of the key fob. The battery is located on one side of the printed circuit board (PCB).
- Locate the Battery: In the 2003 BMW 325xi key fob, the battery is typically a Panasonic VL2020. It’s a coin-cell rechargeable battery with custom leads tack-welded to the top (positive) and bottom (negative) terminals for easy soldering onto the PCB.
3. Removing the Old Battery
Now, you need to carefully remove the old battery from the PCB.
- Secure the PCB: Use wide jaw pliers (Channel-Locks) to grip the PCB. Apply a rubber band around the handles of the pliers to maintain a steady, but not overly tight, grip. Excessive pressure can crack the circuit board.
- Desolder the Leads: Heat up your soldering iron. Apply the hot iron to the back of each battery lead where it’s soldered to the PCB. Wait for the solder to melt, and then gently pull the lead free from the board. Repeat this for both leads.
- Remove the Leads from the Old Battery: Once the battery is detached from the PCB, use a small chisel or pocketknife to carefully pry off the custom leads from the old battery. You’ll need these leads if you are using a standard VL2020 battery without pre-attached tabs.
4. Installing the New Battery
With the old battery removed, it’s time to install the new one.
- Solder the Negative Lead: If your replacement battery doesn’t have pre-attached leads, solder the negative lead (the one with the smaller through-pin) to the bottom (non-writing side) of the new VL2020 battery. Use a minimal amount of solder to ensure a snug fit inside the fob case.
- Resolder the Negative Lead to the PCB: Insert the negative lead back into its designated hole on the PCB (note the smaller pin size for correct orientation) and solder it securely.
- Solder the Positive Lead: Position the battery in the center of the white insulating pad on the PCB. Solder the positive lead to the positive terminal of the new battery and then to its corresponding point on the PCB. The order doesn’t matter if the negative side is correctly connected.
5. Closing and Gluing the Fob Case
Before permanently sealing the case, test the fit and ensure everything aligns properly.
- Test the Fit: Remove the PCB and try mating the two halves of the fob case together. Clean up any frayed plastic edges to ensure a smooth closure.
- Reassemble and Glue: Place the PCB back into one half of the fob case. Carefully align and close the two halves. Apply a thin bead of plastic glue along the perimeter of the fob case.
- Clamp the Case: Use clamps or rubber bands to firmly hold the fob case together while the glue dries completely, as per the glue manufacturer’s instructions.
6. Key Fob Reprogramming (Resequencing)
After replacing the battery, you may need to reprogram (re-sequence) your key fob to your 2003 BMW 325xi. This process ensures the car recognizes the key fob again.
- Prepare for Resequencing: Enter your BMW 325xi, close all doors, and ensure they are unlocked. Have all your key fobs ready. Designate one key as the “initial” key – this is just for clarity in the process.
- Initiate Resequencing: Insert the initial key into the ignition and turn it to position 2 (all dashboard lights are on, but the engine is not started). Remove the key.
- Button Press Sequence: Immediately after removing the key, hold down the unlock button on the key fob. While holding the unlock button, press the lock button three times in quick succession. Release all buttons. The car’s central locking system should respond by locking the doors and then unlocking the driver’s door to confirm successful sequencing.
- Repeat for Other Keys: Grab the next key fob and repeat the button press sequence (holding unlock and pressing lock three times). Do this for all your BMW 325xi key fobs.
Important Note: Any key fob you do not re-sequence during this process will not function correctly. You’ll need to repeat the entire re-sequencing procedure to include any missed keys.
Conclusion
Congratulations! You’ve successfully replaced the battery in your 2003 BMW 325xi key fob. By following these steps, you’ve saved money and gained a valuable DIY skill. Your key fob should now be working reliably, allowing you to lock, unlock, and use your BMW with ease. Enjoy the peace of mind knowing you’ve tackled this common BMW maintenance task yourself!
