C5 Program Spare Key With Lexia

JohnD · Post by **JohnD** » 20 Sep 2010, 10:45

Paul-R wrote:

What exactly do you mean by that?

He took the swivel base of the key out of the plip and replaced something inside the base. And yes! I've tried several times pair the new key with car, but it never works.

Post by **Paul-R** » 20 Sep 2010, 10:54

In that case it sounds like he somehow replaced the embedded transponder. Which means that neither the key transponder nor locking transmitter that you bought worked!

wheeler · Post by **wheeler** » 20 Sep 2010, 13:09

Im fairly sure transponder chips can only have a code written to them once & what JohnD says seems to back that up.
Only a virgin transponder chip can be programed to a new car which seems to have been confirmed by the mobile auto lockie.
However a key that has been previously deleted will re sync back to the same car.

Post by **Paul-R** » 20 Sep 2010, 14:27

JohnD

How much did the mobile locksmith charge for putting the new transponder in the key?

Wheeler

How is the transponder on the key coded? Does this mean that all keys for a car have the same transponder code? I wouldn't have thought so as this would mean that synching one would synch them all.

If they're different where would the locksmith have obtained a new code from? Is it something that is generated randomnly from a program somehow?

And finally, if it is new code this brings us back to the question of why a key from another can't be synched as how would the ECU know whether it was a previously used key or not?

JohnD · Post by **JohnD** » 20 Sep 2010, 15:57

Paul-R wrote:JohnD

How much did the mobile locksmith charge for putting the new transponder in the key?

Altogether £65+VAT - but as I said previously, he was with me for nearly one & half hours.

wheeler · Post by **wheeler** » 21 Sep 2010, 00:03

Paul-R wrote: Wheeler

How is the transponder on the key coded?

The aerial round the ignition barrel has a writing coil as well as a reading coil so it is written from this when you tell lexia what the code is.

Paul-R wrote: Does this mean that all keys for a car have the same transponder code? I wouldn't have thought so as this would mean that synching one would synch them all.

The transponder chips are completely blank when new, you have to tell the chip the code thats stored in the cars injection ECU & the BSI (which is the code on the card). The codes in the key,ECU & BSI must match for the car to start. The same code is written to each key & an individual identifier must also be written at the same time as the BSI can tell which key is being used if you look at the paramiters on lexia.

Paul-R wrote:And finally, if it is new code this brings us back to the question of why a key from another can't be synched as how would the ECU know whether it was a previously used key or not?

As far as im aware the key code can only be written to a chip once, if a key is 'erased' by lexia it doesent actually wipe the data from the chip, The cars BSI just ignores it as it will know it's previously been 'erased'. Hence the reason an old key can be 'Re-programed' back to the same car again.

Post by **RichardW** » 21 Sep 2010, 08:10

Ah, an interesting post wheeler - I had pretty much come to the conclusion that there must a write function on the immobiliser coil, reading between the lines. So I think we can sumarise the situation, as there is much confusion - not least on my part

So, there are 2 separate electronic parts to the key fob: The immobiliser chip (which is passive) and the remote locking part (which is active).

There are at least 2 'codes': one, the four digit 'access' code required by Lexia to allow the setting of new keys, and a multi digit code which allows key cutting without copying an original. There is another code on the back of the access code card, but the function of this is unclear

although it appears to end in the access code for the Lexia.

In order to code a key to a car, 2 operations are required: 1: write the immobiliser code to the key chip, and 2: teach the BSI to recognise the remote locking code.

Item 1: is a one shot operation, once the code is written to a chip, it cannot be overwritten. However, it appears some locksmiths can supply blank chips which can be written with the correct code.

Item 2: can be done with a Lexia for any key - this will allow the key to open the car, but unless 1: is done, then they key will not start the car.

So, buying second hand keys is caveat emptor - if they have been coded to a car, they cannot be recoded (for immobiliser unlocking!) unless the chip is replaced. If you are just replacing a non functional remote section, it might be possible to swap the immobiliser chip over to the new key fob, and just code in the remote part.

What did I miss

Post by **Paul-R** » 21 Sep 2010, 09:25

Must agree with Richard, top post there Wheeler and helps to clear some of the fog that surrounds this.

I was completely unaware of the write coil but that now explains a huge amount.

Now to search for blank transponder chips!

wheeler · Post by **wheeler** » 21 Sep 2010, 12:08

Should also point out that that info is specific to the C5 & most other modern citroens/peugeots with a BSI but is only general for other makes & models. For example on the Relay 2 & 3 (which uses a fiat imobiliser system) if a new key is programed all the other keys for the van must be present & re-synced at the same time otherwise they will never be able to be re programed to the van again. Whereas with the citroen BSI system if you dont have any of the spare keys present & they are 'deleted' You can re add them at a later date. The relay 2 & 3's also have an additional code for pairing the plip only which must be done with a diagnostic machine.
The C1 uses a toyota system & there is no user confidential code for the transponder, they are just programed with a Lexia procedure.

Good luck with the blank transponder chip search, they all look the same but there are loads of different types but only the correct one will program.

MikeT · Post by **MikeT** » 21 Sep 2010, 12:27

I've been trying to learn about this transponder "write" technology but have come up blank so far so if anyone's got any links, I'd be grateful.

What I have found is that the C5 (2001-2005) uses the SX9EH type key from Silica (or is a 3rd party equivalent), if that helps source the right type?

acrowot · Post by **acrowot** » 21 Sep 2010, 15:28

Went to the locksmith today, not impressed at all,first off he said the transponder code on the back of the keycard was not the same as the code under the security label, I am so sure he said that I will bet you £100.00 that there is a 32 digit code under there, he proceeded to remove the security strip to reveal the 4 digit code that was on the back, no £100.00 forthcoming though. He then stated that the chip was not a one shot and he could reprog. it, failed. I then asked him could he program me a single key that would manually unlock the doors and start the car, he said it would be better if he sorted out my scrappy fob as I would then have remote unlocking as well, I said I do not think the remote would work but he disputed this. He then replaced the chip and it will now manually unlock my car and start it but no remote, cost £55.00 not impressed. Same senario as JohnD.

wheeler · Post by **wheeler** » 21 Sep 2010, 16:30

Sounds like one of the guys thats done a 5 day 'auto locksmith' course, bought a chineese clone key programming machine off ebay & is now a 'qualified' auto locksmith.

acrowot · Post by **acrowot** » 21 Sep 2010, 16:55

wheeler wrote:Sounds like one of the guys thats done a 5 day 'auto locksmith' course, bought a chineese clone key programming machine off ebay & is now a 'qualified' auto locksmith.

You would think that Wheeler but this shop had at least 5 serving it was never empty in the 3 hours I was there, the amount of equipment they had in the shop was impressive keyreaders various cutters and electronic equipment larger than my Lexia or the Snapon diagnostic equipment I have seen in garages, at least 3 vans for mobile use, they of course don't ony do cars. Strangely this is the shop I rang initially and they told me the chips in the fobs were one shot. The point I am trying to make is that this was no one man band.

Post by **Paul-R** » 21 Sep 2010, 19:03

acrowot wrote:He then stated that the chip was not a one shot and he could reprog. it, failed.

It may be that he is half right. Following the info from MikeT about the SX9EH I googled around and found one data sheet which said that the chip in a certain range of keys could be written to a maximum of three times. It's possible he thought all could do this.

MikeT · Post by **MikeT** » 22 Sep 2010, 15:06

Paul-R wrote:It may be that he is half right. Following the info from MikeT about the SX9EH I googled around and found one data sheet which said that the chip in a certain range of keys could be written to a maximum of three times. It's possible he thought all could do this.

I read that too but noted it was referring to "writing" to the transponder (key chip) via a copying machine, not via the car's ECU.