BECM part.
Immobilisation Code: Only used on EDC and Motronic engine Management Systems
(EMS). When the ignition is turned on, the BECM, providing it is in receipt of a valid
mobilization code, from receiving an unlock signal from the correct key fob or having its
EKA code entered, and is therefore not in an alarmed or immobilised state, sends a
coded signal to the Engine Management System (EMS) ECU and in turn, the EMS ECU then compares against a code it already has stored in it. If the two codes compare OK,
the EMS ECU allows the engine to start. This forms the basis of the immobiliser. If the
EMS ECU or the BECM is replaced, the two codes will not match and it will not be
possible to start the engine. It is therefore necessary to synchronise the codes in both the BECM and the EMS ECU. For EDC, a function can be found in the EDC section which
gives the fixed code from the EDC ECU which must be entered here. For GEMS, any
number can be used here as the GEMS ECU has a learn function located in the OTHER
section which can be used to force it to learn this code. A valid number is between 0 and
65535.
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I guess as long as I write down each code I can always write it back again if I make a mistake!