Temporary fix if you have only one key?

[JB]

We were only given one key when we purchased our 9-3 Aero convertible (MY 2002) recently. A second key has been on order for a while, but it hasn't turned up yet. I've checked on the car and it does have two keys and transponders registered to it. I can only guess that one of the previous owners has lost one key.

I know that we'd have a big problem if we lost that one key (which is of the all-in-one type) as one key is needed to program (or de-program) others to the car, so I've had an idea. We've also got a 9-5 (MY 2000) and we've got both keys for that (with separate fob). Would it be possible to program the spare 9-5 key (fob and transponder) to the 9-3 as an emergency electronic 'backup'. I know that it wouldn't work physically as the blade is different, but would it work electronically? When the second key eventually turns up then we'd simply program that and remove the 9-5 key and have two proper working keys.

My understanding is that you program the car to recognise the key. Not the other way around. So the 9-5 simply wouldn't know that one of its keys will also operate the 9-3. And the 9-5 key wouldn't know that it's been programmed to two cars.

Your thoughts, as always, are welcome? Is the idea complete rubbish or would it work?

[sgould]

I don't think it works like that.

One key in the ignition will allow the Tech 2 computer to access the car's security system.  Then the Tech 2 generates a new random(?) code that is copied onto all the keys present at that session.

So if you program one of the 9-5 keys to the 9-3, it will only work in the 9-3 and you end up with only one key that will work in the 9-5.

If it worked as you say, then any stolen key would always work in the car.

[Audax]

Yes, that would work. I accidentally did this once before and had a keyfob that would open my car and the scrapper that the key had come from. It caused me more than a few issues when leaving work in the evening...

[ScarbSaab]

If it worked as you say, then any stolen key would always work in the car.

No, because the car maintains a list of keys it will accept. If a key is not present when reprogramming takes place, it is deleted from the list and is ignored. Physically it would still open the car but the remote will be ignored as will the RFID transponder necessary to release the immobiliser.

I may be wrong, but as I understand it, the protocol used is KeeLoQ, which generates a rolling code. This is why the remotes can get out of sync. These remotes are unidirectional rather than a challenge/response system which would not need a rolling code.

[sgould]

I don't understand this.... 

OK the physical key will always work.  If I lose a key, then the old key can always open the car. I can understand that.

But if I lose a key and then take my single key to the dealer along with a new key.  Then the existing key goes in the lock and Tech2 opens the system.  Then the dealer programmes a code to both keys (or what ever).

After this, I can press the button on the key and SID says "2 Transponders, 2 Remotes".  So what stops the old key still working if you have done the new coding?

What is unique about each key that is recognised by TWICE?

[Audax]

You don't program keys, you program the TWICE, the key just sends a signal and you program TWICE to accept that signal. The whole point is that once you reprogram then the TWICE will refuse to recognise the old key.   

[sgould]

So, effectively each key has a unique "number"?

I've just been confused all these years.............. and it will only get worse at my age!! 

[JB]

So the idea is fundamentally correct then. 

The spare 9-5 key could be programmed to also become the spare 9-3 key (electronically only of course). And when the new 9-3 key has arrived, it will be programmed to be recognised by TWICE and the 9-5 key will be 'forgotten' on the 9-3, but will still work on the 9-5.

[Audax]

Yup, that's correct. 

[sgould]

But then it will always work and you will open both cars whether you want to or not.

So you open the cars in the drive, drive off down the road out of range, walk back and lock the other car........

[Audax]

So you open the cars in the drive, drive off down the road out of range, walk back and lock the other car........

I already alluded to that scenario when I said about the scrapper I took a transponder from.... depending on where I parked it would unlock when I locked my car but more often than not as I walked out to get in my car it would unlock too resulting in me having to drive down the road and walk back to lock the thing. After a while I disconnected the battery on it 

[Geoff1951]

I don't understand this.... 

If you don't, Will, then not much hope for the rest of us then!

[Audax]

So, effectively each key has a unique "number"?

Yes, the keys have different transponder numbers in them and through some cryptographic magic it works out if they should open or not. Read http://auto.howstuffworks.com/remote-entry2.htm for more on how it works, explained for more simply than I could do.

[win_k]

Yes, one (or both) of your 9-5 keys could be programmed into your TWICE along with the existing key you've got for the car.

As long as you've got a tech who can do the work for reasonable money, it's a great bit of insurance for a lost key.

Probably the only possible drawback would be the 9-3 responding to a button press when locking or un-locking the 9-5 if they are close enough. 

I've got a Tech 2 and have programmed all three of my 9-3's to include a master key.  It's an used remote key that I cut the blade off of.  Will unlock the doors, boot and satisfy the TWICE on all 3 cars.  Cheap insurance.

[JB]

Been a little while, but finally got it done so I thought I'd report back.

My indie said that it wouldn't work and the spare 9-5 key would no longer work on the 9-5 if it was programmed to the 9-3, but they did it anyway (saying they'd program it back to the 9-5 when (!) it didn't work as I expected).

The long and short of it is that IT DOES WORK.  I took the 9-3 down to my indie who programmed the 9-5 key to the 9-3. They had to lift up the transponder aerial on the car so that the 9-5 key could be read as it won't physically turn the ignition lock on the 9-3, but that was the only thing that had to be done. When I got home I tested the remote fob and it does indeed lock and unlock both cars. And the key transponder is recognised by the 9-5 as OK and starts the engine too.

So all I need now is a physical copy of the 9-3 key and we're sorted for an emergency spare key whilst still waiting for a proper spare key to arrive. My indie is having real problems in getting hold of keys for the older 9-3 models. The new ones (without a blade) are fine, but not the older type. Does anybody know where to get hold of one?