Alfa Romeo Repair: Ignition Immobiliser Problems, volatile data, negative battery

Question
Hi

I have a 2000 156 2.0 TS saloon. Recently the immobiliser (yellow light key) indicator stays on, and whilst the engine will turn over, the immobiliser deos not allow the engine to start. If I turn the key to the preignition stage repeatedly eventually the light turns off and the car will start.

Any ideas / suggestions greatly appreciated. Moreover is it expensive to remedy!!

Many thanks

Ed

Answer
I am in the usa  and have no information on that system.
However, before going to the dealer try this:

disconnect the negative lead at the battery.  Wait a half hour and then touch the negative lead to the positive lead for 10 to 20 seconds.  Then reattache the negative lead to the negative battery terminal.

If the vehicle will now start, drive ten miles so the computer can reprogram volatile data.