Is your 2004 BMW key fob starting to act up? Are you experiencing frustrating moments where you have to press the buttons multiple times, or stand right next to your car for it to respond? You’re not alone. Many BMW owners with this model year encounter issues with their key fobs as the battery life dwindles. Before you rush to a dealership and face potentially hefty replacement costs, consider this: you can replace the battery yourself. This guide provides a step-by-step walkthrough for a 2004 BMW key fob battery replacement, saving you time and money.
The original key fob battery is not designed to be recharged by the car while in operation, despite some urban legends suggesting otherwise. There’s no electrical connection for recharging. The most common culprit for a failing key fob is simply a dead battery. This DIY fix focuses on replacing that battery and getting your key fob working like new again.
Let’s get started with the tools and the process to bring your 2004 BMW key fob back to life.
First, you’ll need to carefully open the glued-shut key fob case. This requires patience and the right tools.
Tools You’ll Need:
- Vice-grip
- Paint scraper
- Sharp knife
- Small tipped soldering iron
- Silver solder
- Small chisel or pocketknife
- Wide jaw pliers (Channel-Locks)
- Rubber band
- Panasonic VL2020 battery (with or without leads – plain battery recommended)
- Plastic glue
Step-by-Step 2004 BMW Key Fob Battery Replacement:
Step 1: Opening the Key Fob
The BMW key fob case is securely glued, requiring a careful approach to open it without damage. Begin by using the paint scraper at the key ring end of the fob. Securely hold the metal key part using the vice-grips. Carefully use the sharp knife to slice along the seam of the fob while gently prying with the scraper. Work slowly and methodically around the perimeter until you create a crack and can separate the two halves of the fob case.
Image alt text: Opened 2004 BMW key fob showing the internal components after carefully prying apart the glued case.
Step 2: Identifying the Battery
Once the case is open, you’ll see the internal components. The battery is located on one side of the PCB (Printed Circuit Board). In the original key fob, you’ll find a Panasonic VL 2020 battery with custom leads that are tack-welded to the positive and negative terminals. Note the orientation of the battery and the placement of the positive and negative leads before removal.
Image alt text: Close-up of the BMW key fob printed circuit board (PCB) highlighting the location of the VL2020 battery and the positive and negative lead attachments.
Step 3: Removing the Old Battery
To remove the old battery, you will need your soldering iron and pliers. Grip the PCB with the wide jaw pliers. To maintain pressure without over-tightening and potentially damaging the board, use a rubber band wrapped around the handles of the pliers.
Apply heat from the soldering iron to the points where the battery leads are soldered to the PCB on the back of the board. Wait for the solder to melt, then gently pull the battery lead free from the PCB. Repeat this for both leads. Once the battery is detached from the PCB, use the chisel or knife to carefully pry the custom leads off the old battery itself. If you are using a plain VL2020 battery without pre-attached leads for replacement, this step prepares you for soldering directly to the new battery.
Step 4: Soldering the New Battery
Take your new VL2020 battery (plain battery recommended for easier soldering) and the custom leads you removed from the old battery. Solder the negative lead to the flat side of the new battery (the side without markings). Use a minimal amount of silver solder to ensure a tight fit inside the fob case.
Next, re-solder the negative lead back onto the PCB, ensuring it goes into the correct pinhole (the smaller of the two). Double-check the orientation, referencing the original battery placement. When the negative lead is secured, the battery should sit within the white insulating pad on the component side of the PCB. Now, solder the positive lead in place, connecting it to both the battery and the PCB. The order of soldering (battery side first or PCB side first) is not critical if the negative side is correctly connected.
Step 5: Reassembling the Key Fob
Before gluing the fob back together, clean any rough edges on the inside of the case halves to ensure a clean closure. Test fit the two halves of the fob case without the PCB inside to confirm they mate correctly. Apply a thin bead of plastic glue to the perimeter of one half of the fob. Carefully place the PCB back into position in one half of the case, then align and press the two halves together. Use clamps or rubber bands to hold the case firmly together while the glue dries, following the glue manufacturer’s recommended drying time.
Step 6: Re-syncing Your BMW Key Fob (Re-sequencing)
After the glue has dried and the fob is reassembled, you’ll need to re-sync the key fob to your 2004 BMW. This process, sometimes called re-sequencing, ensures your car recognizes the key fob again.
Here’s how to re-sync your BMW key fob:
- Enter your BMW and close all doors. Ensure doors are unlocked.
- Insert your first key into the ignition and turn it to position 2 (ignition on, all dash lights illuminated, but engine not started).
- Remove the key from the ignition.
- Immediately press and hold 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, typically by locking and then unlocking the doors.
- If you have additional key fobs, repeat steps 4-6 for each key within 30 seconds.
Conclusion: Save Money with DIY Key Fob Battery Replacement
Replacing the battery in your 2004 BMW key fob is a straightforward DIY task that can save you a significant amount of money compared to dealership replacement services. By following these steps and taking your time, you can restore your key fob’s functionality and avoid the expense of a new key or professional service. With a little patience and careful work, your 2004 BMW key fob will be working reliably once again.
