Member Since: 19 Apr 2012
Location: Melbourne, Victoria
Posts: 85
A central locking fix
I've learned from this excellent forum there are several reasons the central system can stop working, either completely of (more often) intermittently. Mine has been driving me mad for a couple of years. One minute a key would work, two minutes later it wouldn't work.
Finally, after trying several suggestions I found the fault (the cause of your problem may be different).
I had previously renewed the key fob cases and done what some others have done and put some packing behind the battery. That seemed to work for some reason, but not forever. Both key fobs had become increasingly unreliable.
Most recently I delved into the wiring loom to find and renew the green/white wire splice as discussed in this post, but that didn't help. (My splice was in very good condition and it was clear that some sort of sealant had been used in conjunction with the heat shrink sleeve).
I thought perhaps there may be some dry joints on the circuit boards inside the key fobs. Fortunately the fob cases I now have snap together and use a locking screw, so I was able to take them apart quite easily. I re-soldered a couple of joints that looked suspect on the surface mounted micro switches, but that didn't help. I also made sure both keys were charged and checked the battery voltages. I was looking at the battery terminal tabs that come through the circuit board because someone mentioned re-flowing the solder on these had fixed the problem for them. The joints looked good, but then I noticed I could move the battery slightly away from the circuit board. On further inspection with a magnifier I discovered that the negative battery tab was broken between the battery and the circuit board. This explains why putting packing behind the battery in the key fob can sometimes be a cure. The same goes for tapping the fob on something.
After de-soldering the (wider) positive battery tab I was able to remove the battery in its plastic holder from the circuit board on both key fobs. The narrower negative battery tab was broken on both of my key fobs!
My solution was to hard wire the negative connection. I used thin flexible multi-strand wire soldered to the broken tab on the battery and the negative terminal on the circuit board. I felt this would be more resilient than a rigid connection. See photos below. Both key fobs now work faultlessly.
If you are doing this job I suggest you use a very fine soldering iron and fine solder to minimise the risk of damaging the circuit board or the battery. I used a miniature soldering iron with a 1.25mm tip and 0.5mm solder. You'll also need a solder sucker, some suitable wire and new key fob cases if you haven't already replaced the original ones with fob cases that can be re-opened.
I hope this helps someone!
Kevin
Click image to enlarge
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2007 Land Rover LR3 4.0L V6
Other current other cars
2022 BMW X3 xDrive 30i
2000 Mercedes ML430 (enjoying the challenge of keeping it going!)
1973 Bristol 411 S5
If you are interested in Bristols (the cars), click on my WWW button below...
27th Oct 2021 7:24 am
Bungle
Member Since: 07 Apr 2015
Location: Wanborough
Posts: 254
Have you got a link to the re-closable key cases? I always struggle to glue mine closed....
28th Oct 2021 2:38 pm
nivekau
Member Since: 19 Apr 2012
Location: Melbourne, Victoria
Posts: 85
I know what you mean. The first ones I bought needed to be glued and not only did I make a right mess of them, but the fob cases soon came apart again.
Unfortunately I bought the ones that snap together and include a screw years ago, and eBay's purchase history doesn't go back far enough. I know I bought them from Hong Kong/China and the item name was:
"Folding Key Case for LAND ROVER Range Rover Sport LR3 Discovery Flip Fob 3 BTN"
I'm pretty sure they were sold as a pair rather than individually.
I suggest you do an ebay search using "LR3 Discovery Flip Fob 3 BTN" and look an compare the pictures to the ones of mine below and ask the seller if the cases snap together or require glue. Note the small Phillips head screw to the left of the lettering on the side of the key.
Click image to enlarge
2007 Land Rover LR3 4.0L V6
Other current other cars
2022 BMW X3 xDrive 30i
2000 Mercedes ML430 (enjoying the challenge of keeping it going!)
1973 Bristol 411 S5
If you are interested in Bristols (the cars), click on my WWW button below...
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