Experiencing issues with your BMW 328i key fob after a battery replacement? You’re not alone. Many BMW owners encounter problems after attempting a DIY battery swap, and it can be frustrating when your key fob suddenly stops working correctly. This guide will walk you through common pitfalls and troubleshooting steps to get your BMW 328i key fob functioning again.
It’s a common scenario: the dreaded “key battery low” warning appears on your dashboard, prompting you to replace the battery in your BMW 328i key fob. Like many resourceful owners, you might decide to tackle this yourself. Perhaps you followed a tutorial, carefully unsoldered the old battery, and soldered in a fresh one, maybe even upgrading the key shell for a fresh look. But then, the unexpected happens – your key fob no longer locks or unlocks the doors or trunk. It might even still start the car, adding to the confusion.
If you’ve found yourself in this situation, don’t panic. Let’s explore some potential reasons why your BMW 328i key fob might have stopped working after a battery replacement:
Common Mistakes and Troubleshooting Steps:
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Soldering Issues: Soldering these small batteries requires precision. A poor solder joint is a prime suspect. Even if you tested the new battery with a multimeter and it reads 3V, a weak connection can prevent sufficient power delivery.
- Action: Carefully inspect your solder points. Ensure they are clean, solid, and making good contact with the battery terminals. If you’re not confident in your soldering, consider seeking help from someone with micro-soldering experience.
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Battery Polarity: While less likely with modern batteries designed for specific orientations, double-check that you installed the new battery with the correct polarity (+ and -). Refer to the markings on the old battery and the key fob circuit board.
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Case Interference: If you replaced the key shell, it’s possible the new case is pressing on components inside the key fob, causing a malfunction.
- Action: Try operating the key fob without the case. Carefully remove the circuit board from the shell and test its functionality. If it works outside the case, the issue likely lies with the new shell.
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Battery Compatibility: You mentioned using an ML2020 battery after the original VL2020. While these are often considered compatible in terms of size and voltage, subtle differences could exist. However, in most cases, this shouldn’t be the primary issue, especially if the car starts.
- Action: Re-verify the battery specifications for your BMW 328i key fob. While VL2020 and ML2020 are common replacements, ensuring you have the correct type is essential.
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Accidental Damage: During the battery replacement process, it’s possible to accidentally damage delicate components on the circuit board.
- Action: Carefully examine the circuit board for any visible damage, such as scratches, broken components, or lifted pads. If you spot damage, professional repair might be necessary.
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Key Fob Re-pairing (Less Likely in This Scenario): In some rare cases, after a battery disconnect, a key fob might need to be re-paired with the car. However, since your key starts the car, this is less likely the issue here, as the immobilizer chip is still being recognized.
Alt text: Close-up of a BMW key fob being opened for battery replacement, showcasing the internal components and battery.
What to Do Next:
- Re-examine your work: Go back through each step of your battery replacement process. Double-check soldering, polarity, and for any signs of damage.
- Try the original battery again (carefully): You mentioned even the old battery stopped working after re-installation. Ensure the contacts are clean and making good contact. Sometimes, reseating the battery can resolve minor connection issues.
- Seek Professional Help: If you’ve exhausted DIY troubleshooting and are still facing issues, it’s best to consult a professional. A locksmith specializing in car keys or a BMW dealership can diagnose the problem and offer solutions, which might range from professional key fob repair to replacement.
Replacing your Bmw 328i Key Fob Battery can be a straightforward DIY task, but sometimes, things can go wrong. By systematically troubleshooting and considering these common issues, you can increase your chances of resolving the problem and getting your key fob back in working order. Remember to prioritize careful handling and seek professional assistance when needed to avoid further complications.
