Dave,
A common misconception. The alarm/central locking and the immobiliser (CODE) systems are entirely seperate systems - it's easy to get them confused though because they both live in the key itself.
The alarm is an active radio transmitter (the big circuit board) operated by the button on the key that disarms the alarm (electric detection, microwave sensors etc.). The immobiliser is a passive tiny RFID chip also in the key head, usually glued in near the key shank itself to allow it to be more easily detected by the short aerial within the ignition switch/barrel.
What it looks like is one of 2 things has happened.
- The CODE system has gone into "self test" mode which it does occasionally according to the manual and you simply take the key away from the ignition switch (I usually take it about 2m away to ensure full loss of RFID signal), wait a few seconds and take it back. However, you probably wouldn't be shouting for help here if that was the case sincve you probably tried something similar.
- The "pairing" between the chip in that particular key and the ECU (I think that means the main car ECU) has been lost. If that's the case then allandwf's suggestion of using another key will work until it either resets itself like it did for him or you can get that key "re-paired". Another alternative, if you don't have another key is the possibility that you have the grey CODE card which came with the car from new which has a 4 digit number on it to override the immobiliser in this situation, it's a somewhat convoluted series of steps involving turning the ignition on and off a lot of times with the 4 digit number involved in the counting. The sequence is in the car handbook and if you don't have a handbook then I or one of the other SM members will be able to relay the procedure to you.
If the "pairing" has been lost completely, it is possible to "re-pair" the RFID chip in that key using the mythical "Red Key". There is another sequence in the workshop manual (not the owner's manual) where the Red key is inserted first and then ALL existing keys in your possesion are re-identified to the ECU. This is the process used if a key is stolen where all of the keys in your posession are re-identified but of course the stolen key is NOT registered and hence no longer valid and it won't start the vehicle even if it can unlock the doors and de-activate the alarm. The Red Key does not have an alarm circuit board so cannot de-activate the alarm system but it does have a special RFID chip in it which will start the car and/or initiate the "pairing" sequence. The Red Key pairing sequence would certainly recover your key if the pairing has been lost.
Now if you have more more than one key that is problematic then there is an ECU problem and that is somewhat more serious obviously.
Come back to me if you need either the sequence for the CODE override (assuming you have the grey card number) or want the Red Key re-programming sequence.
I hope this helps.
Cheers
