Changing your BMW 328i key fob battery at home can seem like a straightforward task, but sometimes things don’t go as planned. Many 2009 BMW 328i owners attempt DIY key fob battery replacement to save money and time, only to encounter issues afterward. One common problem is that after replacing the battery, the key fob might stop working correctly, or even entirely, for remote functions like locking and unlocking doors, or in some cases, starting the vehicle.
If you’ve recently replaced the battery in your 2009 BMW 328i key fob and are now facing issues where it no longer operates the door locks or starts your car, you’re not alone. Let’s delve into some potential reasons why this might be happening and explore troubleshooting steps you can take.
One of the first steps many DIYers take is replacing the key fob battery themselves. The standard procedure often involves opening the key fob casing and replacing the internal battery. You might have followed online guides, perhaps even one showing a similar process, to ensure you were doing it correctly. However, even with careful execution, problems can arise.
A user recently shared their experience after a DIY battery replacement on a BMW key fob. They replaced the original VL2020 Panasonic battery with a new ML2020 Panasonic battery, and even tried reverting to the old battery, but the key fob ceased to operate the door locks or trunk release. Interestingly, the car would still start when using the key, indicating the transponder chip for ignition was still functional, but the remote locking/unlocking functionality was lost.
Potential Issues After BMW Key Fob Battery Replacement
Several factors can contribute to a key fob malfunction after a battery change:
- Incorrect Battery Type: While the user in question used ML2020 which is similar in specification to VL2020, subtle differences might exist that could affect performance in specific key fob circuits. Always double-check the manufacturer’s recommendation for your specific BMW key fob model.
- Soldering Issues: Many BMW key fobs, especially older models like the 2009 328i, require soldering to replace the battery. If you attempted to desolder and resolder the battery yourself, a cold solder joint, bridged connections, or damage from excessive heat could have occurred. Even if you followed a video guide, soldering requires precision, and mistakes can happen.
- Key Fob Circuit Damage: During the battery replacement process, especially when opening the key fob casing or handling the internal components, it’s possible to accidentally damage delicate circuits or components within the key fob. Static discharge, physical stress, or improper tools could lead to damage.
- Battery Polarity: Although less likely with modern batteries, ensuring the correct polarity when installing the new battery is crucial. Reversing polarity can damage the key fob circuitry.
- Key Fob Resynchronization: In some cases, after a battery change, the key fob might need to be resynchronized with the car’s immobilizer system. This is less common after a simple battery swap but is a possibility, especially if the battery was left out for an extended period.
Troubleshooting Steps for Your 2009 BMW 328i Key Fob
If you’re facing a non-functional key fob after a battery replacement, here are some steps to troubleshoot:
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Verify Battery Voltage: You mentioned testing the battery with a multimeter and confirming 3V, which is good. However, re-verify with a different multimeter if possible, or try a known good new battery of the correct type (VL2020 if that was original, or confirm the correct replacement type for your specific key fob).
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Inspect Solder Joints (if applicable): If you soldered the battery, carefully examine the solder joints with a magnifying glass. Look for:
- Cold Solder Joints: Dull, grainy, or cracked solder joints indicate a poor connection.
- Solder Bridges: Solder unintentionally connecting adjacent pins or components.
- Excessive Solder: Too much solder can also cause problems.
If you suspect soldering issues and are not experienced with electronics repair, it’s best to seek professional help.
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Visually Inspect the Circuit Board: Carefully examine the key fob’s circuit board for any signs of damage:
- Cracks or Breaks: Look for any visible cracks or breaks in the circuit board.
- Burnt Components: Check for any components that look burnt, discolored, or damaged.
- Loose Components: Ensure all components are securely attached to the board.
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Resynchronization Procedure: Consult your 2009 BMW 328i owner’s manual for key fob resynchronization procedures. BMW procedures can vary, but often involve a sequence of button presses and ignition key turns performed in a specific timeframe. While less likely to be the issue after just a battery change, it’s worth trying.
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Check Key Fob Shell Interference: Although you replaced the shell, ensure the new shell isn’t pressing on any buttons or components inside the key fob when closed. Try operating the key fob with the shell slightly open or even without the shell (carefully) to rule out any mechanical interference.
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Seek Professional Diagnostic Help: If you’ve tried these steps and your key fob still isn’t working, it’s likely there’s a more complex issue, possibly requiring professional diagnostic equipment. A qualified automotive locksmith or a BMW dealership service center can diagnose the problem. They have specialized tools to test the key fob’s RF signal, communication with the car’s computer, and identify any deeper electronic faults.
When DIY Turns to Professional Help
While DIY battery replacement can save money, when it leads to complications, seeking professional help is often the most efficient solution. Professionals have the expertise and equipment to:
- Diagnose Key Fob Issues Accurately: They can pinpoint whether the problem is with the key fob itself, the car’s receiver module, or programming issues.
- Program New Key Fobs: If the key fob is beyond repair, they can program a new 2009 Bmw 328i Key Fob Replacement to work with your car.
- Offer Key Fob Repair Services: Some specialists offer key fob repair services, which might be more cost-effective than full replacement in certain situations.
Don’t hesitate to contact a reputable locksmith specializing in automotive keys or your local BMW dealer for assistance. They can provide the expert help needed to get your 2009 BMW 328i key fob functioning correctly again.
