Old Remote Key Fob into New Car?

[Paul-R]

There's just so much clutter on this subject that it's difficult to sort through. People are free and easy using the term "fob" without being specific on whether it's the blade/ID46 or plip.

[cancunia]

Agreed, there's certainly a lot of discussion on this subject and not a lot of conclusions. I thought that a fob with a new ID61 transponder should work after pairing and it's why I asked if anyone had success. There's always the chance that the fob is also somehow encoded when the keys are paired to the car.

[cancunia]

On the subject of the transponder chip (PCF7936AA), it was discontinued by NXP in 2010, so chances are that all the ones you see for sale are now copies from China. NXP have confirmed the EOL dates, but the source of current ones is a guess on my part.
Given that most Diagbox hardware and a lot of (genuine) semi conductor stuff seems to come from China these days, I don't suppose it's too much of a biggie that a part of the key does too.

[Hell Razor5543]

Oops, sorry. I got him confused with a former member whose name began BenC5.

[GiveMeABreak]

Here's a place that supply the fobs with blank transponder chips - they have quite a selection, but you need a log in to view pricing - here's a link to the Citroen ones including your Berlingo just a thought, but I'd guess they would have to be cheaper than the dealers...
https://www.aldridgesecurity.co.uk/c-2576-citroen.aspx

[cancunia]

Thanks for the link Marc. Looks like you have to be trade to get a login, or at least give a lot of details. As I'm not really desperate atm, I'll give it a miss for now.

[cancunia]

So, I really should get a life and will aim to make that one of my resolutions.
After reading a lot more this afternoon, I've come to the conclusion that it's not possible to simply put a new transponder chip into a remote keyfob and expect the remote to work when you initialise via the Lexia instructions. It seems that the remotes & transponders are paired at the factory with some of the remote data being encoded / encrypted into the transponder. The Lexia instructions involve having the key in the lock when you press the remote, I'm guessing that the remote serial number is being compared the the encoded data in the transponder. That's probably why it's possible to buy pre-paired fobs & transponders which will be capable of being registered to a car via Diagbox / Lexia. I think that new transponders will work on keys without fobs but am not sure about new transponders in old fobs being able to start the engine.

The Lexia instructions differ from the instructions I've read elsewhere on ebay so there's maybe still a chance that you can use old keyfobs...

Lexia:

Put the HF key to be synchronised in position "ignition +"
Within the next 10 seconds, press one of the HF key buttons
Release the HF key button
The ignition key HF PLIP is synchronised.

eBay:

1. Turn the Ignition switch to accessory position using the key, without the remote attached.
2. Hold the remote towards the receiver at the front of the vehicle.
3. Press the large button, then the small button on the remote.
4. Repeat for second remote key if required.
5. Turn ignition OFF.
6. After 5 seconds, remote should now operate.



All this is speculation based on what I read over the past day or so. I might just for fun buy a keyfob from China and see if it works, but unless someone has some direct experience of using old fobs, it's not something I have confidence in working.

[GiveMeABreak]

Never heard of the second procedure at all, but the first one just resynchronises the key and won't have anything to do with the coding. The rolling code of the remote control is modified each time it's used and allows for a small offset between the code expected by the receiver and what is transmitted. This has to do with using the remote outside the range of the receiver. It allows for about 255 offsets and if this is exceeded it needs resynchronising by putting the key in, ignition on and holding a button down within 10 seconds.

[Hell Razor5543]

The second procedure would be for an IR system, as opposed to the RF system used in Series 2 Xantias and up.

[GiveMeABreak]

The second procedure would be for an IR system, as opposed to the RF system used in Series 2 Xantias and up.

Now we're going back IR! - XM / Xantia days!

[cancunia]

The second procedure would be for an IR system, as opposed to the RF system used in Series 2 Xantias and up.

Well, not according to this, it was in one of my earlier posts but that was quite a few posts ago...:

http://www.ebay.co.uk/gds/Citroen-Key-K ... 635/g.html

[Paul-R]

I've come to the conclusion that it's not possible to simply put a new transponder chip into a remote keyfob and expect the remote to work when you initialise via the Lexia instructions. It seems that the remotes & transponders are paired at the factory with some of the remote data being encoded / encrypted into the transponder.

As I've said before I disagree. But I'm obviously not going to persuade you.

The Lexia instructions involve having the key in the lock when you press the remote, I'm guessing that the remote serial number is being compared the the encoded data in the transponder.

This is precisely the confusion I'm talking about. You're conflating the key pairing with the remote door locking.

[cancunia]

As I've said before I disagree. But I'm obviously not going to persuade you.
You're conflating the key pairing with the remote door locking

Honestly, I'm totally happy to be persuaded, but after what I've read, only by someone's direct experience. Everything I've written is based on what I've read & so far I've not read anyone - on any forum - saying "this is how it's done" or "this is how I did it"! Honestly, I'd like to know how because that's why I started this thread

On the second point, I only pasted the part about lock / unlock pairing from the Citroen document, but the whole text talks about adding keys, part of which would be the pairing of the door locking. The point was that the Citroen instructions have the key in the lock with the ignition on (i.e. transponder active) when pairing the lock / unlock. The second set of 'ebay' instructions have a very different approach and may well be pointing to the way that you can re-use old fobs.

[Hell Razor5543]

The keys in todays' cars (the electronics, that is) serve 2 purposes.

The complex electronics manage the central locking (and some other functions; I can raise or lower the windows in my C5 using the key fob), and this is where you have the key in the ignition, 'M' position, and pressing buttons to pair the central locking key circuits with the car. The reason this pairing is kept simple is for when you have to change the battery in the fob.

The simple electronics (typically housed in a small capsule) contain the code that the immobiliser circuits look for when the key is turned in the ignition (if the right code is present the car is allowed to start, otherwise it won't). This second stage has to be done via the Lexia (and needs the security card), as you are introducing the keys to the car. Part of the reason for this is the security aspect. Would you be happy if somebody could read the VIN of a car (which is clearly visible through the windscreen), get a key cut, and then drive off with your car? No, neither would I.

[jgra1]

right now I have a peugeot from 2004.. I am not desperate to do anything (like cancunia) but this is the situation:

i do not have confidential code
I do have an old key buried in the ignition (so any fitting key will start her)
the 4 or 5 door locks look to have been rendered useless (I will have to change them soon)
it would be great to use remote locking for the above reason..

as I have the basics in place I may try an old fob .. I cant quite see what harm it would do
i realise this may be missing the point of the thread somewhat... for sure the immobiliser chip is write once read many from what I gather..