Land Rover Discovery 2 Keyfob dead - Page 1
Forum section: electronics / repair

author: finisterre
author_rank: Newbie
timestamp: April 09, 2020, 05:44:49 am
content: Hi all,My 2002 Land Rover Discovery 2 keyfob died on me the other week, which was most unreasonable, considering it was only 18 years old!Anyway, in normal operation, pressing buttons normally flashes an LED to show it working. New battery made no difference. Key also not recognised to disable the immobiliser in ignition.Is there any way to diagnose or repair these things or are the most common faults with the chip itself?Anyway, total newbie in electronics troubleshooting with only a very basic understanding on some components.I have attached 2 photos of the Valeo unit, but is there anything I can do to simply check for common or cheap components failing?Thanks!Darren

author: Mario87
author_rank: Frequent Contributor
timestamp: April 09, 2020, 08:21:08 am
content: It might not be a problem with the key, it could well be a "feature". On Audi's (even ones 14-ish years old) when the battery goes dead the key loses it's synchronization with the car. There is a special procedure you need to do that involves turning the ignition on then off with a good key, followed by inserting the key that needs re-programmed and turning the ignition on then off 3 times in a row or something similar. I can't remember exact details off the top of my head.Check online and see if your cars keys have something similar. The Audi keys when they lose their programming will not unlock or lock doors remotely (only by inserting the key into the door) and will not start the engine until re-programmed.Yours may well be the same??

author: Manul
author_rank: Super Contributor
timestamp: April 09, 2020, 09:34:57 am
content: It looks to me, that there is some residue on the board. Remove sticker from IC and wash the board really good in isopropyl alcohol, let it soak. You can use a very soft brush to help that (I use soft hair watarcolor brushes for artists). Shake lightly a few times and let it dry good.It could be as simple as contamination or a cracked solder joint.After washing please add a good picture of the board made from top, so that all the board is in focus.

author: finisterre
author_rank: Newbie
timestamp: April 09, 2020, 10:20:27 am
content: These keys are fairly simple in their operation. The code is stored in the car's BCU (it has room for 4 codes) and doesn't do anything fancy with proximity or anything, so if a battery goes dead (it has before a few times) then the range/responsiveness falls away and the LED gets dim. This one failed suddenly without any diminishing performance. The slightly iffy soldering is from when I replaced the buttons a few years ago and only had a 30W iron :-)

author: Manul
author_rank: Super Contributor
timestamp: April 09, 2020, 10:41:08 am
content: If you changed these buttons, then congratulations it looks like a decent job. Still suggest to clean it. Have you tried to measure current while you operate the remote?

author: Psi
author_rank: Super Contributor
timestamp: April 09, 2020, 10:44:18 am
content: If it was me i would check the main chip oscillator is working using a scope. (that white 6 pad device with the metal dome top)Crystals can break due to mechanical shock, which is common with a keyfob. They get dropped and thrown around a lot.I would also measure the current draw, mA/uA, and see if it changes when you press the button or not.Less likely but also possible is that yellow tantalum cap as gone dead short.

author: finisterre
author_rank: Newbie
timestamp: April 09, 2020, 11:13:32 am
content: Cleaned with Throttle Body & Carby cleaner as Alcohol non-existent :-)Still no sign of life, as expected, and here's a better picture. Tricky to do with a 2017 Nokia phone and a desk mounted LED magnifying glass!

author: m3vuv
author_rank: Super Contributor
timestamp: April 09, 2020, 11:16:17 am
content: these have a rolling code,normaly its a main dealer job to re sync them with the vehicle.

author: JoeyG
author_rank: Regular Contributor
timestamp: April 09, 2020, 11:22:01 am
content: I would tend to agree

author: senso
author_rank: Frequent Contributor
timestamp: April 09, 2020, 11:28:20 am
content: Try this:QuoteFrom here:https://www.landyzone.co.uk/land-rover/disco-ii-key-programming.21559/

author: finisterre
author_rank: Newbie
timestamp: April 09, 2020, 11:34:16 am
content: This key is still 'registered' with the vehicle, so just needs to be brought back alive - I have a friend that can program extra keys into the BCU (max of 4) but I'd really rather get this original key working than have to buy new ones - maybe it's me being cheap, but I prefer to say I hate wasting something that could be potentially fixed :-)

author: Manul
author_rank: Super Contributor
timestamp: April 09, 2020, 11:35:39 am
content: The question is - even if it has sync issue, would it not blink internal LED? I expect it should. The remote itself should not care about sync. Interested in current measurement and then possibly some other measurements.

author: finisterre
author_rank: Newbie
timestamp: April 09, 2020, 11:36:45 am
content: I have a friend with a Nanocom, but no spare keys (the spare (working fob) got lost, hence my predicament with an unlocked car, but no working keyfob!) so reprogramming the BCU with a new key is doable, but the key is absolutely dead, the button press should still light the LED, even if it is nowhere near the car.

author: finisterre
author_rank: Newbie
timestamp: April 09, 2020, 11:38:45 am
content: Okay, so for a total noob, please could someone give me step-by-step instructions on what pins to check with multimeter - I don't have oscilloscope unfortunately, so I can only measure basic things like voltage, amperage, continuity etc.

author: Manul
author_rank: Super Contributor
timestamp: April 09, 2020, 11:49:21 am
content: If you like for testing purpose you can solder two small wires on the board to the + and - battery points. To be able to power it externally througth these wires. It will make current measurment setup more easy. Then connect battery or other 3 volts source with a multimeter in series and measure standby current and also current when you press the buttons.

author: Psi
author_rank: Super Contributor
timestamp: April 09, 2020, 12:09:57 pm
content: You could try a momentary sort across the pushbutton to simulate a press.If the button itself is dead this will flash the LED and transmit.The push buttons can die from old age or being pressed too hard.

author: Manul
author_rank: Super Contributor
timestamp: April 09, 2020, 12:11:46 pm
content: Current measurment:

author: voltsandjolts
author_rank: Unknown
timestamp: April 09, 2020, 12:26:45 pm
content: Hmmm, watch out for DMM burden voltage when measuring low currents.

author: finisterre
author_rank: Newbie
timestamp: April 10, 2020, 01:00:56 am
content: Okay, did some testing (once I dug out the multimeter)Bare battery 2.949v, voltage on the pins shown by Manul 2.888vTested button continuity, worked fine. Tried manually shorting button, no difference.When button pressed 2.793v shown.So looks like something is happening as far as the button press is concerned, but no LED, no car response.Multimeter is a Digitech QM1323 (don't roast me, was all I could get at short notice)

author: Manul
author_rank: Super Contributor
timestamp: April 10, 2020, 10:34:26 am
content: Ok, that was also useful information. But what I had in mind is to measure current in miliamps. So you remove battery from key fob holder and connect everything like in picture. Battery is external and multimeter in series set to mA. I'm not the best to explain, but hope you got it.

author: finisterre
author_rank: Newbie
timestamp: April 11, 2020, 03:59:39 am
content: I'll have a go, finding a 3v power source that I can hook up without needing 4 hands is the challenge :-)

author: Psi
author_rank: Super Contributor
timestamp: April 11, 2020, 06:54:47 am
content: It's odd you get no LED flash.Afaik it's not 2 way RF, so the keyfob has no way to know if it's synced or not.The LED flashing should be working unless there is a fault on the PCB.