Experiencing issues with your 2009 Bmw 328i Key Fob after a battery replacement can be frustrating. Many BMW owners encounter a situation where, after diligently replacing the key fob battery, the remote functions suddenly cease to operate. You might find yourself in a predicament where your key starts the ignition perfectly fine, but stubbornly refuses to lock or unlock your doors, or pop the trunk remotely.
This article delves into the common problems and troubleshooting steps for a 2009 BMW 328i key fob that has stopped working correctly following a battery replacement. We’ll explore potential pitfalls during the DIY battery replacement process and guide you towards restoring your key fob’s full functionality.
Common Scenarios After 2009 BMW 328i Key Fob Battery Replacement
It’s a frequent scenario: the dreaded “low key battery” warning appears on your BMW 328i dashboard. Promptly, you decide to tackle the battery replacement yourself. Online resources often suggest opening the key fob, desoldering the old battery, and soldering in a fresh one. Perhaps you even invested in a new key fob shell to avoid the hassle of re-gluing the original casing.
However, after meticulously completing the battery swap, you might be met with disappointment. The key fob might start the car without issue, a small victory, but the convenience of remote locking, unlocking, and trunk access is gone. You might even double-check the new battery with a multimeter, confirming a healthy 3V reading. Frantically, you might revert to the old battery, the one that prompted the initial replacement, only to find it now also fails to operate the remote functions. Even trying the bare chip, outside of any casing pressure, yields no improvement.
This situation leaves many BMW 328i owners scratching their heads, wondering, “Where did I go wrong with my 2009 BMW 328i key fob battery replacement?”
Potential Issues and Troubleshooting Steps
Let’s break down the potential culprits behind a malfunctioning 2009 BMW 328i key fob after a battery change and explore troubleshooting steps:
1. Battery Polarity Reversal
- The Problem: Even if the battery physically fits, installing it with reversed polarity can prevent the key fob from working. While modern electronics often have some protection against reverse polarity, it’s still a primary check.
- Troubleshooting: Carefully examine the battery compartment within your 2009 BMW 328i key fob. There are usually markings (+ and -) indicating the correct battery orientation. Ensure the positive (+) and negative (-) terminals of your new battery align with these markings. If you soldered the battery, double-check the polarity of your solder connections.
2. Soldering Issues
- The Problem: Soldering the battery requires precision. Cold solder joints (weak connections due to insufficient heat), or solder bridges (unintended connections between points) can disrupt the circuit.
- Troubleshooting:
- Visual Inspection: Use a magnifying glass to closely inspect your solder joints. They should be shiny and smooth, not dull or lumpy. Look for any unintended solder connections bridging different components.
- Resoldering: If you suspect a cold solder joint, carefully reheat the joint and apply a tiny bit more solder if needed to ensure a solid connection. If you see a solder bridge, use solder wick or a desoldering tool to carefully remove the excess solder.
- Professional Help: If you’re not comfortable with soldering or suspect you might have damaged the circuit board, consider seeking professional help from a key fob repair service or an electronics technician.
3. Battery Compatibility
- The Problem: While the original post mentions VL2020 and ML2020 Panasonic batteries, and they are likely compatible in terms of size and voltage, subtle differences could exist. Less likely, but worth considering.
- Troubleshooting:
- Verify Battery Type: Double-check that the replacement battery is indeed the correct type for your 2009 BMW 328i key fob. Consult your owner’s manual or search online for the recommended battery type.
- New Battery Test: Try a different new battery of the correct type to rule out a faulty new battery as the issue.
4. Key Fob Damage During Opening/Closing
- The Problem: Key fobs, especially older ones like those for a 2009 BMW 328i, can become brittle over time. Opening and closing the fob case, particularly if it was glued, can potentially damage internal components, especially if excessive force was used.
- Troubleshooting:
- Visual Inspection: Carefully examine the circuit board for any visible cracks, breaks, or dislodged components. Pay close attention to the area around where you opened the case.
- Gentle Handling: When reassembling the key fob, ensure all components are correctly aligned and avoid forcing the case closed.
5. Key Fob Reprogramming/Resyncing (Less Likely After Battery Change)
- The Problem: In some rare cases, disconnecting power from the key fob might require a resyncing process with the car. This is less common with simple battery changes compared to situations where the key fob’s memory is corrupted.
- Troubleshooting:
- BMW Key Resync Procedure: Consult your 2009 BMW 328i owner’s manual for key resynchronization instructions. This often involves a sequence of button presses and ignition key turns performed inside the vehicle.
- Professional Programming: If resyncing doesn’t work, the key fob might require reprogramming, which usually necessitates specialized equipment and can be done at a BMW dealership or a qualified automotive locksmith. However, rule out other issues first, as reprogramming is less likely after a simple battery change.
6. New Key Fob Shell Interference (Unlikely but Possible)
- The Problem: While a new key fob shell is intended to be a direct replacement, slight variations in manufacturing could, in very rare cases, cause pressure on internal components.
- Troubleshooting:
- Test Without Shell: Try operating the key fob without the new shell, just with the circuit board and battery. If it works, the new shell might be exerting unintended pressure. If this is the case, carefully inspect the shell for any imperfections or excess plastic that might be interfering.
Seeking Professional Assistance
If you’ve diligently followed these troubleshooting steps and your 2009 BMW 328i key fob remote functions are still unresponsive, it might be time to seek professional help.
- Automotive Locksmith: A skilled automotive locksmith specializing in key fobs often possesses the diagnostic tools and expertise to pinpoint the problem, whether it’s a deeper electronic issue within the key fob or a potential programming problem.
- BMW Dealership: Your local BMW dealership can also diagnose key fob issues and offer repair or replacement services. However, dealership services can sometimes be more expensive than locksmith options.
Conclusion
Resolving a non-functional 2009 BMW 328i key fob after a battery change often involves careful troubleshooting and attention to detail. By systematically checking battery polarity, solder connections, and for any signs of damage, you can often identify and rectify the issue. Remember to consult your BMW owner’s manual for specific key resyncing procedures and consider professional assistance if DIY troubleshooting proves unsuccessful. With the right approach, you can restore the convenience of your key fob’s remote functions and get back to enjoying your BMW 328i.
