Hi everyone,
I’m encountering a frustrating problem after attempting to replace the battery in my 2009 BMW 335i key fob. My car’s dashboard started displaying a “key battery low” message, prompting me to take action. After some research, I learned that many people successfully replace the battery by opening the key fob, desoldering the old battery, and soldering in a new one. I even purchased a new key shell case to avoid having to glue the original one back together, as it’s originally sealed.
Following a video tutorial, I replaced the original Panasonic VL2020 battery with a new Panasonic ML2020 battery. However, after the replacement, the key fob completely stopped working for locking/unlocking doors or the trunk. Strangely, it still starts the car without any issue.
To troubleshoot, I tested both the new ML2020 and the original VL2020 batteries with a multimeter, and both are showing a reading of 3 Volts, which seems normal. I even tried reinstalling the original battery, which was working perfectly fine (except for the low battery warning) before the replacement, but now it also fails to operate the door locks or trunk. I also tried using the chip without the case, thinking the new case might be pressing on something internally, but that didn’t change anything.
I’m at a loss and wondering if anyone has experienced a similar issue or has any ideas on where I might have gone wrong during this seemingly straightforward 2009 Bmw 335i Key Fob Battery replacement process. Any advice or suggestions would be greatly appreciated!
