No, didn't even glance at the gauge. Simply by feel - the car simply would not 'go', to use a vernacular. The gauge, my engineer friend reported, had been showing nothing since the turbo had cut out, and when I did my quick 'dash' down the road it was like driving molasses. There was no start/stop with the turbo; the sequence of events is that my friend was driving and had gone 400-odd km, then the turbo began to lag (driving through a town and moreso than previously) and then the car went into limp; the turbo gauge remained at zero; and foot to the floor was getting him about 15kph, in fact going up a hill he crawled along at about 5kph. Much the same when I drove it - started the engine, foot on the floor, and almost no response.
As for the actual turbo, I can't actually report what the physical error was, I was merely told by the rep at the dealer that the turbo had been taken apart and found to be faulty, and they'd installed and tuned another one.
Since that point however they have gone over the entire engine both with eyes and hands and with a digital camera, and have found that the tone wheel on the crankshaft has been physically damaged and has been interrupting the air intake - the physical damage is likely due to a poor (rough!) sensor replacement in the past - this dealer took the 159 as a trade in, checked it over and then resold to me, was not their original car/serviced by them. Otherwise everything appears to be immaculate, nothing seems to have been ingested or any other damage done.
At this point in time there is a replacement tone wheel on an air freight somewhere between Italy and Australia and is projected to arrive here on Tuesday. The engine is already out and the tech is waiting for the part to arrive before reassembling the jigsaw.
My reference to switching off was simply meaning seeing if the car would drop out of limp mode once power cycled, as advised by Alfa when I called them from the roadside. To state otherwise; I'm looking forward to driving the car when all is working again.