156TS 1.8 has been giving error codes on MES, but with help from this forum, the culprit seemed to be a 'flat' battery, because MES reported only 12.15V available to the ECU.
But when I removed the battery for charging I checked the terminal voltage which showed 12.51V i.e over 75% charge (at 15oC).
Having removed the battery I charged it up anyway, then let it 'rest' for a couple of days to check that it was holding its charge - it was - drifting down over 48hours from 12.65V to 12.60V. A 'good' battery would you say?
I put the battery back in the car, cleaned and greased the terminals with heatsink stuff, connected up and re-checked the voltage which was now 12.51V with no load from radio (fuse removed) or alarm system. Huh?
Into the car, key 'on' and after stepper motors had initialised, key 'off', wait a minute, then key 'on'.
Plugged into MES on the lappy and thankfully no error codes. On to Parameters - see screenshot - and voltage at ECU is 12.22V
Not believing MES I took a reading from the cigar lighter which was 12.19V - well on the way to a 'flat' battery voltage, and similar to the problem-causing low voltage that was the root of all my troubles of a week ago.
Armed with all this information, I'm thinking there must be Forum members out there that will be able to set me on the path to solving the 'missing voltage' problem, and giving my Alfa the juice she needs to enter her second decade with a fully functioning electrical system.