DIY: E46 Key Battery Replacement

[johnjmurray]

Urban Legend: The key battery recharges from the car in operation. I don't see how this is possible. There is no direct electrical connection between the key and the battery. If any of you have reliable documentation to the contrary, cough it up.

My key started getting wonky. It would take a bunch of presses on the buttons to actuate the features. I had to be standing right up to the car for the key to operate. Finally, it just stopped working. I couldn't re-sequence it and it wouldn't work the security system even inside the cabin.

The are the steps I took to replace the battery in the key fob.

The fob is glued shut. You'll need a vice-grip, paint scraper, and a sharp knife to open it. I started with the scraper in the ring end. Hold the metal key with the vice-grip and carefully slice and pry with the knife to crack the fob case open.

http://forums.bimmerforums.com/forum...pictureid=1348

The battery in mine was a Panasonic VL 2020 with custom leads tack-welded to the top (positive) and bottom (negative). I can give you the link where I bought my replacement but I would suggest just googling the manuf/part. It seems there are some shipping restrictions on this product. Find yourself a close supplier. Note: The shipping was more than the battery itself. I purchased a replacement with leads already on. In hindsight, a plain battery would work better for this operation; that is, no pre-applied leads on the replacement.

The 'back' the PCB has the micro switches on it; the battery sits on the other side. You can just make out the battery well in the key half of the open fob. The negative lead is at the upper left and the positive comes through at the upper right. The two leads are keyed with different sizes where they penetrate the board.

http://forums.bimmerforums.com/forum...pictureid=1347

To effect replacement of the battery, you'll need a soldering iron (preferably a small tipped one), some silver solder, a small chisel or pocketknife, wide jaw pliers like Channel-Locks, and a rubber band. Grip the PCB with the pliers and apply the rubber band to the handles to hold the pressure. DO NOT make this too tight. You could crack the board. This is electronics, not plumbing.

Apply the hot iron to the back of each existing battery lead until the solder melts and you can pull the lead free. Once the battery/lead combo is free, use the chisel or knife to pry off the custom leads from the old battery. Solder the negative lead to the bottom of the new battery (without the writing). Don't use too much solder. The fit inside the fob is very tight. Now re-solder the negative lead back to the PCB. Note: the negative side custom lead has a smaller through-pin than the positive one. Double-check your orientation.

When the negative lead is properly connected, the battery should be sitting in the middle of the white insulating pad (you'll see this on the 'front' of the PCB). Now you can solder in the positive lead. Start with the battery end or the circuit board end; it shouldn't matter if you did the negative side correctly.

Clean up any frayed edges on the fob to make ready for gluing. Make sure you can successfully mate the halves without the PCB in place. Get some brand new, high quality plastic glue ready. Put the board back in the fob and make sure the halves still mate up. Have clamps or rubber bands handy. I have some little quick-grip clamps from woodworking that were just right for this job. Apply a thin bead of glue to the perimeter of the fob and clamp it for whatever duration is recommended on the glue bottle.

Time to re-sequence.
Get all the fob keys you have. My unit came with two. Pick out a key that will get designated as the initial key. (This is NOT a competition among your keys for supremacy. It is just to make the sequencing clear. I used the key that stays at home as the initial.)

Inside the car, with the doors closed and unlocked.
Insert the initial key and turn it to position 2 (when all the dash lights come on but the car doesn't start).
Remove the initial from the keyway and hold down the unlock button. Strike the lock button three times in a row, then let go all the buttons.
The CLS should respond by locking the doors and unlocking the driver's door.
Grab the next key and redo the button presses (repeat for all the keys you have).

Note: Any key you own that doesn't get sequenced at this time will not operate correctly. You will need to re-sequence all the keys over again to bring in the one.

Drive off. We're done here...

[danewilson77]

Bimmer wiki....

http://www.bimmerfest.com/wiki/index...not_working.3F

Remote lock/unlock on your key not working?


Try re-initializing your key:

• Get in and close all doors. Turn on the ingition and turn off quickly. (No more than 5 seconds) to start the process. Next action must take place within 30 seconds. Remove the 1st key. Hold the key up near your left shoulder (this is so it is closer to the remote reciever antenna - someone else suggested this). 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.
• 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. "

Another thing you can do is to replace the battery! It's not officially possible (or recommended) for the new key design (2000+) but it can be done. Instructions can be found in this thread.

How reliable is the info? IDK.....alot of good stuff on here though. I have never found anything wrong with the info, but haven't dissected it all either.....

This is what the owners manual states.....You may download a copy of the 2001 e46 manual here...at this website to verify what I have said...

http://www.linquist.net/motorsports/bmw/3manuals

Just sayin...I think you are incorrect in what you said in your first statement above, but I do commend you on your diy...

"There is an extended-life battery
in every master key that is
charged automatically in the ignition
lock as you drive.
For this reason, if you have a master
key that is not being used otherwise,
use those keys approximately once a
year while driving for an extended
period to charge the battery, refer also

to page 29.<"

[johnjmurray]

That's cool, Dane. I'm not the foremost authority, just a guy with a continuity meter. The bentley's doesn't mention recharging but it does have a passage on re-sequencing...

[johnjmurray]

Sorry to report that my key has gone wrong. It still works the remote locking mechanism but will no longer start the car. Perhaps the reason I couldn't get electrical continuity is because I messed up some internal connection while prying apart the halves. I didn't see anything obvious but...
The 'new' key was working fine for about a month, then it just went off. (Luckily, I was at home at the time so I could pinch the wife's spare.)

[jmoberley]

Thanks for the DIY. Maybe some day the aftermarket will provide us with a housing that allows us to swap batteries.

I put a standard CR-2025 in mine. We'll see how long it lasts.

[budget76]

tagging this for later, sad to hear yours stopped working, maybe I'll get lucky and the one I have will just need re-sequenced

[bmw42ofus]

Thanks for the info......will keep handy!

[johnathan1]

Just to add some VERY useful info to this "DIY"... the custom leads that are TACK-WELDED onto the battery most definitely cannot be heated with a soldering iron and removed. Even if you were to actually pry them off, you could not solder them onto the shiny flat face of the battery. This is why they were TACK-WELDED from the factory lol.

Just get a new rechargeable battery that has the custom leads already attached!! Yes, the key is rechargeable. It uses inductive charging, kind of like an electric toothbrush, or like a "wireless" charging pad for your phone.

[js22]

Thanks for this thread. It worked for me (finally.)

I ordered the VL2020 rechargeable battery from Ebay, shipped on the slow boat from China. Although I specifically ordered the 90 degree lead orientation, I received leads that were 180 apart. I bent the top one backwards and salvaged some of the old leads that the PO left inside my key and made it work.

Note: The battery I received was also a teeny tiny bit too large in diameter, so I had to whittle away a bit of plastic to make it fit. The key was already pretty beat up so I just used hot glue to seal it up.

By this time I had completely forgotten about the magic sync procedure. I just tried using the key as a remote and it didn't work. Spent time woring on other things until a thread on BF jogged my memory. This morning I performed the magic ritual and it works like a charm!

[tcpomeroy]

Was skeptical, but this procedure worked!!! Thanks for posting!!!

Bimmer wiki....

http://www.bimmerfest.com/wiki/index...not_working.3F

Remote lock/unlock on your key not working?


Try re-initializing your key:

• Get in and close all doors. Turn on the ingition and turn off quickly. (No more than 5 seconds) to start the process. Next action must take place within 30 seconds. Remove the 1st key. Hold the key up near your left shoulder (this is so it is closer to the remote reciever antenna - someone else suggested this). 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.
• 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. "

Another thing you can do is to replace the battery! It's not officially possible (or recommended) for the new key design (2000+) but it can be done. Instructions can be found in this thread.

How reliable is the info? IDK.....alot of good stuff on here though. I have never found anything wrong with the info, but haven't dissected it all either.....

This is what the owners manual states.....You may download a copy of the 2001 e46 manual here...at this website to verify what I have said...

http://www.linquist.net/motorsports/bmw/3manuals

Just sayin...I think you are incorrect in what you said in your first statement above, but I do commend you on your diy...

"There is an extended-life battery
in every master key that is
charged automatically in the ignition
lock as you drive.
For this reason, if you have a master
key that is not being used otherwise,
use those keys approximately once a
year while driving for an extended
period to charge the battery, refer also

to page 29.<"

[martwauto]

I had a similar issue over a year ago with my key, the only one.(Please dont tell me to buy another ,I know)
I got it going again and eventually it stopped working remotely so I used these people ......
https://www.ebay.co.uk/itm/404467741388
No issues and very pleased ta boo
Mart.