replacing battery in key fob....

Wicked! I know this thread is old but its very useful, SO BUMP!

Very useful thread.

I've just fixed my key fob by cutting it open with a pocket knife.
I didn't need a new battery - I just played with it a little and when repackaging I made sure all the battery contacts and battery holder were tighter - using blue-tak.

I currently have the key fob wrapped in tie-wraps and waiting for the super-glue to dry - but it works fine!

I can lock and un-lock from my office window - whereas before the fix it would work next to car.

So in summary - same DIY dix but no new battery needed.

thanks bro

man i cant wait to try this. my key battery is almost up. nice write up

Great DIY!

Turns out the battery in my wife's key wasn't dead after all - it measured 3 volts. There was just a bad solder joint on one of the battery connections - I re-soldered that to the circuit board and it worked great.

Then I replaced the BMW logo roundel in the center of the key and now the key looks and works like new.

Here's a reasonably low-cost way to replace the roundel:

http://forum.e46fanatics.com/showthread.php?p=11475936

Thats awesome!

Got an extra battery pm if you guys need one.

FYI - available from Petros on ebay for $3.99 + $6.00 shipping anywhere. Best deal I found online.

http://cgi.ebay.com/ws/eBayISAPI.dll...=263602_263622

Originally Posted by 1SiK3

Got an extra battery pm if you guys need one.

Ditto.

This is an awesome DIY! Ordered the battery from mouser (got the horizontal one) and followed the instructions. Cutting the key with a sharp utility knife was very easy. It was harder to pry off the spot welds off the old battery. I actually de-soldered the negative from the board and soldered the one with the new battery to the board (had to cut some of the lead). On the positive side I just cut the metal lead off the new battery and used the existing moon shape contact that was in the key soldered to the board. To my surprise when I went to my garage in the morning all the windows and moon roof were opened. I guess with putting the new battery and pressing buttons it unlocked my car! So if you're doing this when you're done go to your car and make sure it's locked if it's outside (I did this at night and did not go to my car until the next morning). I did not have to program my key. Everything just worked. I tested locking, unlocking and trunk and everything was working without programming. Now all I have to do is glue it back together. Thank you!!! You saved me $200!!!

Add me to the list of people who read this great diy and decided to try reprogramming the key before buying a battery. Keys work again. Once I reprogrammed the dead key, it worked but my good key stopped working. I had to do the below procedure and quickly do the second key after the first (cut from an earlier post on this thread):

Have you tried initializing your key?

1 Get in and close all doors.
2 Turn on the ignition and turn off quickly. (No more than 5 seconds) to start the process. Next action must take place within 30 seconds.
3 Remove the 1st key.
4 Hold the key up near your left shoulder (this is so it is closer to the remote reciever antenna - someone else suggested this).
5 Hold down the unlock button (which is button 1 on my key) and press the lock button 3 times (center button on my key). Release the unlock button and the doors lock which confirms the operation.
6 Quickly repeat steps 4 & 5 for key #2 etc.

If it does not work, try doing the keys in opposite order. Key 2 then key1, vs 1 then 2.

Remember to alternate your keys from time to time so that you keep the batteries in both charged.

I replaced the battery, but when trying to initialize/reprogram the key I got no response. The key still starts the car, but will not unlock/lock the doors. Tested voltage on leads and it's +/-3 volts so I know that my solder job was okay. Also checked the voltage on the old battery and it was 3v (so it was okay?). Any ideas?

I have a used key fob from a 5 series car. The battery in that key fob is dead. If i replace the battery in that fob and try to program it to my M3 (close the door, turn key, take out key, hold unlock and press lock 3 times), would it start up the car? I'm having starting issues right now with my current key.

Originally Posted by Mrfurioso

I have a used key fob from a 5 series car. The battery in that key fob is dead. If i replace the battery in that fob and try to program it to my M3 (close the door, turn key, take out key, hold unlock and press lock 3 times), would it start up the car? I'm having starting issues right now with my current key.

Oh by the way, to do this i would cut open my current key, attach the key portion itself with the 5 series key chip and try to program my m3. Can it be done?

Originally Posted by Mrfurioso

Oh by the way, to do this i would cut open my current key, attach the key portion itself with the 5 series key chip and try to program my m3. Can it be done?

You can program it to open the doors but it won't start the car. Each key has a transponder with a code unique to the ECU on the car and it can't be reprogrammed.

Originally Posted by mobes

You can program it to open the doors but it won't start the car. Each key has a transponder with a code unique to the ECU on the car and it can't be reprogrammed.

Thanks. Exactly what i needed to know.

For months I thought my battery was dead, I tried to re-sync it and it was working!!! thanks alot, great thread!!

Originally Posted by SamXp

LOL no way!
I'll tell you one thing about the 80's - you'd be paying $200 for a key at the stealer because there was no internet, other than a handful of newsgroups, and there sure as heck wouldn't be a sweet pictorial DIY like this one, complete with part numbers and links!

Why someone has not figured out how to reprogram a key to work with another car is beyond me. Considering the financial incentive is there with the stealership wanting $200+ for a spare key.
They sell keys on ebay, but supposedly they are a waste of money because they cannot be programmed.

My key stopped working several weeks ago, I opened it and tested the battery with a digital multimeter, and it read 3.3 volts, so it seems alright. But I can't repogram it or get it to work at all. Any further suggestions?

Originally Posted by dvsntt

My key stopped working several weeks ago, I opened it and tested the battery with a digital multimeter, and it read 3.3 volts, so it seems alright. But I can't repogram it or get it to work at all. Any further suggestions?

Same thing happened to me - even swapped the battery and still no luck. Still haven't figured it out, so if you do let me know.