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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > DIY Guides > DIY: Non-Comfort Access Key Fob Battery Replacement



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      02-24-2018, 12:15 PM   #1
Jagaer
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DIY: Non-Comfort Access Key Fob Battery Replacement

I live where it gets cold (-40C). Recently, the key fob would not lock or unlock the car if it got cold, and when I got inside to start the car, the car would start but wouldn't have any of the personalized settings (Ex: Radio Presets).

There are some good pictures available here as well, on how not to do it: https://www.bmwgm5.com/kf_wos.htm

1. Purchase proper battery (Note where the terminals are located, approx 90 degree offset): https://www.ebay.com/itm/NEW-MINI-BM...53.m2749.l2649

2. Cut open fob. The fob itself is fully glued shut. Use a *sharp* X-acto and go slowly. Do not cut too deep or you WILL damage the PCB.


3. Use a non-metallic pry device to add a small bit of tension to the battery, then desolder the corner terminal. I used a credit card, because it was what I had handy. Start with the corner terminal, as the one closer to the middle of the battery has a longer lead, so you won't be able to get under it to apply tension until the corner one is removed.


4. Place the new battery in the PCB battery holes. Hold the PCB by the edges while applying a bit of force down onto the battery. Apply heat to the middle terminal, then the corner terminal and the battery terminals will push through the existing solder into place.


5. Dry fit the PCB into the housing, and test the key. If everything works, good job! If it doesn't...I can't help you, mine worked

6. Either get a shiny new housing for your key fob, or just glue the old one back shut. My car is my DD, and the keys live in my pocket, so I just glued it shut. I used gel-style Cyano-acrylate glue sparingly, since it doesn't run and I don't want to glue the PCB to the housing.

Last edited by Jagaer; 02-24-2018 at 01:38 PM.
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      03-07-2018, 08:36 AM   #2
cgtheboy
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I did this with two different batteries.Checked voltage on both.2.5 and 2.9 . Still won't open doors. Car starts but no locks. Some say drive the car for a while.Havent really taken her for a long ride but still no locks....So on the third battery...Bingo measured it at 3.4 volts . Soldered it in and worked right away. Never could get the others to charge.

Last edited by cgtheboy; 03-12-2018 at 05:50 PM.
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