Dead key

[faddy]

The C5 X7 I bought last week came with two keys and I gave one of them to my non-driver wife. At first her key worked to remotely unlock the car but packed up a couple of days ago and won't start the car either. Assuming its battery's died, would that also stop it deactivating the immobiliser or does it have a passive transponder for that?

[Homer]

I'm pretty certain the transponder would work even with no battery in the fob.

Did it ever start the car?

[GiveMeABreak]

Change the fob battery, but it will need to be reinitialised again once you've done that. Just put the key in and turn the ignition on, press the lock button for up to 10 seconds, release, close door and try locking unlocking.
You can try the reinitialisation routine first - if no luck then replace the fob battery and repeat.

[faddy]

I'm pretty certain the transponder would work even with no battery in the fob.

Did it ever start the car?

My wife doesn't drive so had only used it for remote (un)locking.

[faddy]

Change the fob battery, but it will need to be reinitialised again once you've done that. Just put the key in and turn the ignition on, press the lock button for up to 10 seconds, release, close door and try locking unlocking.
You can try the reinitialisation routine first - if no luck then replace the fob battery and repeat.

Already tried reinitialising, without success. Would you expect a dead battery to have stopped it from starting the car?

[Paul-R]

No, not in the slightest. In fact you can get keys supplied with some of the older models which didn't have remote lock/unlock and could only be used to start the car.

If your spare key won't start the car then you won't be able to reinitialise the lock/unlock by simply inserting it into ignition and going through the process as the car has to acknowledge the key is paired to the car. You may be able to trick the car by inserting your working key into the ignition and then try to reinitialise the remote lock/unlock on the spare.

Ideally, assuming that the spare key originally would start the car, you should re-pair it with the car but that needs a Lexia or Diagbox.

[GiveMeABreak]

Hmmm... Not so sure Paul - this extract (for the X7 at least) would indicate that the Ignition Key Transponder also has some ability to perform a calculation. Probably another reason why the X7 only has the electrical remote fob if this is the case.

First - clarification of the terminology using this diagram:

(1) Ignition key with integral transponder.
(2) Transponder coil .
"a" Ignition key transponder.

Ignition key transponder authentication request
When the ignition key transponder has been identified, the BSI1 sends an ignition key transponder authentication request.

The ignition key authentication request sent by the BSI1 contains :

• A random variable determined by the BSI 1
• A transponder password encrypted using an encrypting function

The transponder password and the "random" variable are determined from the BSI1 code and the ignition key transponder identifier.

N.B. : The BSI1 code is identical to the confidential code written on the customer card but is coded in another form.
The authentication differs from the identification by the fact that the BSI1 and the ignition key transponder perform a calculation with variables which depend on the BSI1 (BSI1 code) and the ignition key identifier.

• As the ignition key transponder receives the authentication request, it performs a calculation.
• The key transponder responds to the BSI1 by sending the result of the authentication calculation which it has just performed.
• Simultaneously, the BSI1 makes a calculation.
• The results calculated by the key transponder and by the BSI 1 are compared.
• If the results are identical, the authentication request is validated, if not then the system remains locked.

If the results are not identical:

• The BSI1 resends a random variable a maximum of 2 times
  
• At the third invalid attempt, 1 minute must elapse before a further authentication request is permitted (anti-scanning function)

So I would certainly start by changing the battery in the key fob, reinitialise and then try.

Incidentally, as an aside - there are 2 types of immobiliser used on the X7:

• An ADC2 - Coded Engine Immobiliser Generation 2
• An ADC2R - Reinforced Generation 2 Coded Immobiliser

They both use the BSI and the Engine Management ECU, but with the reinforced ADC2R, the BSI1 also carries out an exchange (programming + verification) of encrypted codes with the dynamic stability control ECU (ESP).

[faddy]

So I experimented:

1) Swapped batteries between keys.
2) Switched on ignition with dead key. "Electronic Security Fault" displayed. Wouldn't start car, wouldn't initialise (I presume being in Eco mode wouldn't stop key initialising?)
3) Working key, now with hypothetically dead battery, started car and operated RCL without needing initialising (retaining some charge for a short time?).
4) Removed battery from working key, it still started the car.

[GiveMeABreak]

No, eco mode would not stop that. So it would seem that the key does need re-pairing again. It's not uncommon where the owner forgets to bring the spare key along when the garage perform a BSI software update - and so they code just the one key, rendering the spare useless until the keys are re-paired together.

So this is one possible scenario - as long as you have your confidential code, anyone with a Lexia can pair the keys again for you.

[faddy]

No, eco mode would not stop that. So it would seem that the key does need re-pairing again. It's not uncommon where the owner forgets to bring the spare key along when the garage perform a BSI software update - and so they code just the one key, rendering the spare useless until the keys are re-paired together.

But when I first had the car - only last week - the dead key was operating RCL though I don't know whether it would have started the car.

So this is one possible scenario - as long as you have your confidential code, anyone with a Lexia can pair the keys again for you.

No I don't have the code. I'll check with the last owner but I'm not hopeful. Can code be obtained from Citroen if you produce the V5?

[GiveMeABreak]

Yes, it can - you may have to go into the dealer with it and they will obtain it off their secure database (they may charge a small admin fee). You never know, they may be a decent dealer and code it for you at the same time..

[Paul-R]

The scenario I suggested was nothing to with the ignition key transponder as such, it was to try to trick the BSI into accepting the lock/unlock instructions from the faulty key. It would need to have a good battery of course.

[GiveMeABreak]

Yes appreciate that, was just looking into the ignition key transponder for newer vehicles based on your comment as a comparison:

No, not in the slightest. In fact you can get keys supplied with some of the older models which didn't have remote lock/unlock and could only be used to start the car.

I think it's going to need re-pairing at this point, given that message.

[Paul-R]

Agreed. But my quick fix would hopefully get the key to lock/unlock which is all the OP needs for his wife at the moment.

WRT the transponder chip I'm going to pull my fob apart and see if it has the same chip as the Mk1 C5 and Xsara had. I'm curious y'see.

[faddy]

Agreed. But my quick fix would hopefully get the key to lock/unlock which is all the OP needs for his wife at the moment.

Sorry, I should have said - I tried that before I swapped the batteries and had no luck.