DIY Guide: BMW E46 Key Fob Battery Replacement

Is your BMW E46 key fob starting to act up? You’re not alone. Many E46 owners experience issues with their key fobs over time, often indicated by a reduced operating range or needing to press the buttons multiple times. Before you rush to a dealership and spend a fortune on a new key, the solution might be simpler and cheaper than you think: a battery replacement. This guide will walk you through the process of a Bmw E46 Key Fob Battery Replacement, allowing you to restore your key fob to its former glory and save some money in the process.

Recognizing the Signs of a Weak Key Fob Battery

Before diving into the replacement, it’s important to confirm that a dying battery is indeed the culprit. Here are common symptoms indicating your BMW E46 key fob battery is nearing the end of its life:

• Decreased operating range: You need to be much closer to your BMW for the key fob to lock or unlock the doors.
• Intermittent functionality: Sometimes the key fob works perfectly, other times it requires multiple button presses to activate features.
• Complete failure: The key fob stops working altogether, even when standing right next to the car.

If you’re experiencing these issues, a bmw e46 key fob battery replacement is likely the fix.

Essential Tools for Battery Replacement

Replacing the battery in your BMW E46 key fob requires some basic tools and a little patience. Gather the following before you begin:

• Vice-grips: To securely hold the key.
• Paint scraper: For initial prying to start opening the glued casing.
• Sharp knife: A utility knife or similar for carefully slicing along the key fob seam.
• Small tipped soldering iron: For desoldering and soldering the battery leads.
• Silver solder: For making clean and reliable solder joints.
• Small chisel or pocketknife: To help remove the old battery leads.
• Wide jaw pliers (Channel-Locks): To hold the circuit board steady during soldering.
• Rubber band: To apply gentle pressure to the pliers.
• Plastic glue: To re-seal the key fob casing.
• Replacement battery: Panasonic VL2020 with leads (or a plain VL2020 battery and you can reuse the old leads).

Step-by-Step BMW E46 Key Fob Battery Replacement

Now, let’s get to the heart of the matter: replacing the battery. Follow these steps carefully for a successful bmw e46 key fob battery replacement.

Opening the Key Fob Casing

The BMW E46 key fob is notoriously glued shut, requiring a bit of careful force to open.

1. Secure the key: Hold the metal key part firmly using vice-grips. This gives you a stable base to work with.
2. Start with the scraper: Insert the paint scraper into the seam at the ring end of the key fob.
3. Slice and Pry: Carefully use the sharp knife to slice along the seam of the key fob casing while gently prying upwards with the knife or scraper. Work your way around the perimeter, gradually cracking the glued case open. Be patient and avoid applying excessive force to prevent damaging the internal components.

Battery Removal and Lead Detachment

Once the casing is open, you’ll see the circuit board and the battery.

1. Identify the Battery: The battery is typically a Panasonic VL2020 with custom leads soldered to it.
2. Prepare for Desoldering: Grip the PCB (Printed Circuit Board) with wide jaw pliers and secure them gently with a rubber band around the handles. Don’t clamp too tightly, as you could damage the board.
3. Desolder the Leads: Apply the hot soldering iron to the back of each battery lead where it’s soldered to the PCB. Wait for the solder to melt, then gently pull the lead free. Repeat for both positive and negative leads.
4. Remove the Battery: Once both leads are desoldered, carefully remove the old battery.
5. Detach Old Leads (Optional): If you purchased a plain VL2020 battery without leads, use a chisel or knife to carefully pry off the custom leads from the old battery. Be careful not to damage the leads if you intend to reuse them.

Soldering the New Battery

Now it’s time to install the new battery.

1. Solder Negative Lead: Solder the negative lead to the bottom (non-writing side) of the new battery. Use a minimal amount of solder for a clean connection and to maintain a slim profile for fitting back into the fob.
2. Re-solder Negative Lead to PCB: Re-solder the negative lead back to its original position on the PCB. Note that the negative lead usually has a smaller through-pin than the positive one. Double-check the correct orientation.
3. Position the Battery: Ensure the battery sits correctly in the center of the white insulating pad on the ‘front’ of the PCB.
4. Solder Positive Lead: Solder the positive lead. You can solder either the battery end or the circuit board end first. Ensure a solid connection.

Reassembling and Gluing the Key Fob

With the new battery soldered in, it’s time to put everything back together.

1. Clean the Edges: Clean any frayed edges of the key fob casing to ensure a good fit for gluing.
2. Test Fit: Before applying glue, try mating the two halves of the fob together (without the PCB initially, then with it) to ensure they align properly.
3. Apply Glue: Apply a thin, even bead of plastic glue to the perimeter of one half of the fob casing.
4. Clamp the Casing: Carefully align and press the two halves of the key fob together. Use clamps or rubber bands to hold the casing firmly while the glue dries, following the glue manufacturer’s recommended drying time.

Re-sequencing Your BMW E46 Key Fob

After the bmw e46 key fob battery replacement, you’ll need to re-sequence your key fob to your BMW E46. Here’s how:

1. Prepare Keys: Gather all your BMW E46 key fobs.
2. Initial Key: Designate one key as the ‘initial’ key.
3. Get in the Car: Enter your BMW, close all doors, and ensure they are unlocked.
4. Position 2: Insert the ‘initial’ key into the ignition and turn it to position 2 (ignition ON, all dash lights illuminated, but engine not started).
5. Remove Key and Button Press: Remove the ‘initial’ 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.
6. 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 successful sequencing.
7. Repeat for Other Keys: For each additional key fob, repeat step 5 (button presses) within 10 seconds of the previous key’s sequencing.

Important Note: Any key fobs not re-sequenced during this process will not function correctly and will require you to repeat the entire re-sequencing procedure for all keys.

Conclusion

Replacing the battery in your BMW E46 key fob is a straightforward DIY task that can save you a significant amount compared to dealership prices. By following these steps for bmw e46 key fob battery replacement, you can restore your key fob’s functionality and enjoy the convenience of remote locking and unlocking once again. With a little patience and the right tools, you can easily tackle this repair yourself.