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E46 (1999 - 2006)
The fourth generation 3 Series (E46 chassis) was introduced in 1999 and set the standard for engineering and performance during it's years of production including being named to Car & Driver's 10 best list every one of those years! ! -- View the E46 Wiki

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  #1  
Old 01-14-2013, 01:27 PM
buckeroo87 buckeroo87 is offline
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Location: Frome, Somerset
 
Join Date: Jan 2013
Posts: 1
Mein Auto: '02 318i
Smile New member, how i fixed my key fob for free

Hi all, been coming to this site loads for brilliant d.i.y's. I finally have something useful to share back.

My diamond shaped key fob started becoming weak and finally stopped working altogether. I rang BMW to see how much a new battery would cost. They said they were not replaceable and a new key would be needed, 120 plus V.A.T. I didn't want to pay this and having nothing to lose I looked towards a d.i.y.

I bought a new battery of eBay for 4.95, I cut open the key with a kitchen knife (it took about an hour of carefully slicing). I knew the battery was soldered on and I knew there was a 60 second time limit to change batteries. I took the circuit board and new battery to work the next day to let the electrician do the change as it was more his skill. He came back to me saying the battery was the wrong type, he checked the volts on the batteries anyway, the new one was 3 volts, the old one was 3.2. So he knew the old battery was in good condition still and checked the circuit board. He found the negative pin on the underside of the board had a dry solder joint. He cleaned it off and put some new solder on it.

The key worked fine, just superglued the case back on and its perfect, except for a few rough edges from cutting it open. Total cost 4.95, which wasn't needed

I hope this hopes some people as I didn't come across anything like this when googling and searching.
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  #2  
Old 01-14-2013, 01:51 PM
barneyhyphen barneyhyphen is offline
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Location: Nashville, Tn
 
Join Date: Feb 2008
Posts: 89
Mein Auto: 2000 323i sedan
Good job jobbed, well done. HG next!

BH
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  #3  
Old 01-14-2013, 06:23 PM
hitbyastick hitbyastick is offline
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Location: Mont Co MD
 
Join Date: Aug 2012
Posts: 31
Mein Auto: 2002 325i
This is EXACTLY the way it happened in my case. After opening my key, I used a voltmeter to determine the battery was not at fault. It was the thin metal terminal strip which runs underneath the battery; it had broken its solder at the board. I simply reflowed the existing solder and now the key works perfectly.
I suspect a lot of people who have dead keys think the battery is the problem, when it's just a classic case of a cracked solder joint.
I'd even go so far as to say most key failures are due to this, especially when people replace the battery and still cannot get the key to work.
It's worth looking into, and should probably be made a sticky.
Check those solder joints people! I've saved tons reflowing the solder on various relays in the old Volvo 240 wagon I used to beat around in.
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  #4  
Old 01-15-2013, 01:57 PM
barneyhyphen barneyhyphen is offline
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Location: Nashville, Tn
 
Join Date: Feb 2008
Posts: 89
Mein Auto: 2000 323i sedan
Could you please describe how you go about the reflow process? Thanks.

BH
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  #5  
Old 01-16-2013, 08:44 AM
hitbyastick hitbyastick is offline
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Location: Mont Co MD
 
Join Date: Aug 2012
Posts: 31
Mein Auto: 2002 325i
Quote:
Originally Posted by barneyhyphen View Post
Could you please describe how you go about the reflow process? Thanks.

BH
I'd be more than happy to. First, plug the soldering iron into an electrical socket. Then wait for it to heat up. Tin the tip, and briefly touch the tip of the iron to the existing solder joint until it starts to melt then pull it away. That's all there is to it, the cracked solder joint has been melted again or 'reflowed', and electrical conductivity restored. Don't leave the tip on there too long and heatsoak the tiny electronic components on the board. The operation should take 5 seconds.

If you are picky you could use a solder wick or solder sucker to remove the existing solder completely and then replace with a new joint. But for this purpose I believe that approach is overkill, more difficult/time consuming, and introduces more opportunity for screwup.
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  #6  
Old 01-16-2013, 12:45 PM
barneyhyphen barneyhyphen is offline
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Location: Nashville, Tn
 
Join Date: Feb 2008
Posts: 89
Mein Auto: 2000 323i sedan
Gotya, thank you.

I thought you were re-flowing the whole board, rather than just one or two bad joints. I've heard of people re-flowing entire boards in one hit and always wondered how exactly they did that. My daughter's old Exploder had a number of gone bad soldered joints in the radio display and compass/clock assembly but the individual resistors etc were so tiny, trying to re-solder was exceedingly tedious.

Thanks again.

BH
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  #7  
Old 01-16-2013, 03:43 PM
hitbyastick hitbyastick is offline
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Location: Mont Co MD
 
Join Date: Aug 2012
Posts: 31
Mein Auto: 2002 325i
If one is crafty it's possible to reflow all the solder joints on a board by baking in an oven. People bring their XBox 360s back to life using this method.
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  #8  
Old 02-23-2013, 06:05 PM
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bluebee bluebee is offline
Seek to understand,^Value
Location: San Jose, California
 
Join Date: Mar 2008
Posts: 21,835
Mein Auto: 02 BMW 525i M54 auto 130K
If it helps, here are the links we use on the E39 side of the house to repair the diamond key:
- How to replace the old-style BMW square key battery (1) (2) & how to replace the rubber key pads in the square keys (1) (2) & what the red LED indicates on the old square key (1) & what can go wrong with a key and where to send it for repair (1) (2) (3) (4) & what battery to use in the new style 2000+ BMW E39, E46, E53, E85, etc. diamond key (1) (2) (3) (4) (5) (6) (7) & youtube videos of diamond key repairs (1) (2) (3) & a square key to diamond key retrofit and transponder swap (1) (2) (3) (4) & diamond key to square key retrofit questions (1) & how to recharge your key out of your BMW and how long that key will last in the drawer before it needs that off-the-car recharging (1) & the details on swapping the BMW diamond key transponder (1) & the proper diamond key initializing or programming sequence (1) (2) (3) (4) (5) (6) & what to do if your only key is locked inside your bimmer (1) & a description of the various types of BMW Remote, Illuminated, Spare/Wallet, & Valet/Service keys (1) (2) & a list of diamond key EWS, FZV, & DWA functions (1) (2) & all about the 10-key limit to programming your own keys at home (1) & a description of the ignition key ISN (individual serial number) ten-second rule (1) & what to do if you lost your only diamond key (1) or what to do if your BMW key was stolen (1)


__________________
Please read the suggested threads, where the best always add value to those threads, either by pictures or by descriptions, so the next person with the same problem stands on your shoulders.
See also: E39 Bestlinks & How to easily find what you need

Last edited by bluebee; 02-26-2013 at 02:19 AM.
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