Hi, I'm posting this here so that everyone can benefit from my experience...
- Use key card to open central locking
- Insert key
- NO whirr from the steering wheel lock (not a ****y-bird, it didn't even try)
- NO Diesel ignition pre-warming
- SatNav (full-colour screen) bursts in to life
- Immobiliser LED flashing rapidly
- Insert key in to reader, press Start and nothing happens
- Repeat from the beginning with exactly the same result
- Unhappy battery?
- Key problem?
- Keycard reader problem?
- EMC etc.? (in extremis)
Unfortunately, I could not find my spare key. To cut a long story short, after a week I still haven't found my spare key! Bearing this in mind, I could therefore not prove if it was a key or key reader problem. It's unlikely to be a broken EMC because that's just statistically rare. It's unlikely to be a dead battery because all the other electrical items (including energy straining items did not show any sign of struggling). Besides, the car is not accepting the key (by virtue of the fact that the LED is flashing) and it's not even attempting to crank the engine.
Unwilling to get the car towed to a dealer to get a new key/reprogramming etc., I bought a second-hand keycard reader (for about £35 from a breaker) as a 'punt'.
However, when it arrived and I was just about to try it, I inserted the key in to the original reader, the key was accepted, the steering lock feebly attempted to disengage and the pre-ignition tried to light up (but the instrument panel display was very 'weak'). I can hear you all screaming "these are symptoms of a dead battery". So therefore I changed the battery and the whole car burst in to life again.
Just because the immobiliser is telling you there's a problem with the key, there may not be. It may just be "confused" by a low-battery situation.