DIY: Replacing Your 2001 BMW 325i Key Fob Battery

Is your 2001 BMW 325i key fob becoming unreliable? Do you have to press the buttons multiple times, or stand right next to your car for it to work? You might be experiencing the classic symptoms of a dying key fob battery. While some might believe the urban legend that these key fobs recharge while driving, the reality is that they use a standard, replaceable battery. Don’t worry, you don’t need to rush to a dealership and spend a fortune on a new key fob. Replacing the battery yourself is a straightforward DIY task that can save you time and money. This guide will walk you through each step to successfully replace your 2001 Bmw 325i Key Fob Battery and get your remote working like new again.

Tools You’ll Need

Before you begin, gather these tools to make the process smooth and efficient:

• Vice-Grip: To securely hold the key.
• Paint Scraper: For initial prying to separate the fob halves.
• Sharp Knife or Precision Blade: To carefully cut along the glued seam.
• Small Tipped Soldering Iron: For desoldering and soldering the battery leads.
• Silver Solder: For creating secure electrical connections.
• Small Chisel or Pocketknife: To remove old battery leads.
• Wide Jaw Pliers (Channel-Locks): To hold the circuit board steady.
• Rubber Band: To apply gentle pressure to the pliers.
• New VL2020 Battery with Leads: Specifically, a Panasonic VL2020 with pre-attached leads is ideal for this replacement.
• Plastic Glue: To reseal the key fob case.
• Clamps or Rubber Bands: To hold the fob closed while the glue dries.

Step-by-Step Battery Replacement Guide

Follow these steps to carefully replace the battery in your 2001 BMW 325i key fob:

Opening the Key Fob

The BMW key fob is designed to be sealed, so opening it requires some careful maneuvering.

1. Secure the Key: Use the vice-grip to firmly hold the metal key portion of the fob. This provides a stable base to work with.
2. Initial Separation: Start by inserting the paint scraper into the seam near the key ring end of the fob.
3. Slice and Pry: Carefully use the sharp knife or precision blade to slice along the glued seam of the fob casing. Combine slicing with gentle prying motions to gradually crack the case open. Work your way around the entire perimeter of the fob. Be patient and avoid applying excessive force, which could damage the plastic casing or internal components.

Identifying the Battery

Once the fob is open, you’ll see the internal components.

1. Locate the Battery: The battery is located on one side of the printed circuit board (PCB) and sits within a designated battery well. In the 2001 BMW 325i key fob, you’ll find a Panasonic VL 2020 battery.
2. Observe the Leads: Notice the custom leads that are tack-welded to the battery terminals (positive and negative). The negative lead is typically located on the top left, and the positive lead comes through on the top right. Also, observe the size difference of the through-pins for positive and negative leads for correct orientation during re-assembly.

Removing the Old Battery

Carefully remove the old battery from the PCB.

1. Secure the PCB: Grip the PCB with the wide jaw pliers. Use a rubber band around the handles of the pliers to maintain gentle, consistent pressure. Avoid tightening the pliers too much, as excessive force can crack the delicate circuit board.
2. Desolder the Leads: Apply the hot soldering iron to the back of each battery lead on the PCB. Heat the solder until it melts, and then gently pull the lead free from the board. Repeat this for both positive and negative leads.
3. Detach the Leads from the Old Battery: Once the battery/lead combo is free from the PCB, use the small chisel or pocketknife to carefully pry the custom leads off the old battery.

Soldering the New Battery

Now, install the new VL2020 battery.

1. Prepare the New Battery: If you purchased a plain VL2020 battery without leads, you’ll need to solder the leads from the old battery onto the new one. However, for ease of installation, using a replacement VL2020 battery with pre-applied leads is highly recommended.
2. Solder the Negative Lead: Solder the negative lead to the bottom (non-writing side) of the new battery. Use a minimal amount of solder to ensure a tight fit within the fob casing.
3. Re-solder to PCB (Negative): Re-solder the negative lead back to its original position on the PCB. Remember that the negative lead through-pin is typically smaller than the positive one. Double-check the orientation to ensure correct polarity.
4. Solder the Positive Lead: With the negative lead connected, the battery should sit centrally on the white insulating pad on the PCB’s front side. Now, solder the positive lead to both the battery and the corresponding point on the circuit board. The order (battery end or circuit board end first) doesn’t matter if the negative side is correctly connected.

Reassembling the Key Fob

With the new battery installed, you can now reassemble the key fob.

1. Clean the Fob Edges: Clean any frayed edges or debris from the inside edges of the fob halves to ensure a clean and tight seal.
2. Test Fit: Before applying glue, test fit the fob halves together (without the PCB initially, then with it) to ensure they mate correctly and close properly.
3. Apply Glue: Apply a thin, consistent bead of high-quality plastic glue to the perimeter of one half of the fob casing.
4. Clamp and Cure: Carefully align and press the fob halves together. Use clamps or rubber bands to firmly hold the fob closed while the glue dries completely, following the glue manufacturer’s recommended drying time.

Key Fob Re-syncing Instructions

After replacing the battery, you may need to re-sync your key fob with your 2001 BMW 325i. Follow these steps:

1. Prepare Keys: Gather all your BMW key fobs. Designate one key as the ‘initial’ key for clarity (e.g., the one you usually keep at home).
2. Enter the Car: Get inside your BMW, close all doors, and ensure they are unlocked.
3. Ignition Position 2: Insert the ‘initial’ key into the ignition and turn it to position 2 (all dashboard lights are on, but the engine is not started).
4. Remove Key and Button Press: 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.
5. Check for Response: The car’s central locking system (CLS) should respond by locking the doors and then unlocking the driver’s door to confirm synchronization.
6. Repeat for Other Keys: For each additional key fob, repeat step 4 (button press sequence) within 30 seconds of the previous key synchronization.
7. Test All Keys: Test each key fob to ensure it correctly operates the lock/unlock and other remote functions.

Important Note: Any key fob that is not re-synchronized during this procedure will not function correctly and will need to be included in a repeat of the entire synchronization process.

Conclusion

Replacing the 2001 BMW 325i key fob battery is a manageable DIY project. By following these steps and using the right tools, you can restore your key fob’s functionality and avoid unnecessary expenses at the dealership. Enjoy the renewed convenience of your keyless entry and remote functions!