Our 169 used to show some of the symptoms and warning and this was partly cured with coil, leads and plugs. This sounds like a weakness, and the cars eat plugs at a silly rate throwing out warnings at silly intervals. I have some more Fiat plugs in stock, but will not be buying any more as they seem poor.
We further identified a lot of sludge in the inlet manifold. I removed the throttle body and cleaned it out with clean rag. The effect was profound. I would certainly check this. I removed the air filter box and opened the throttle with a crew driver. It was swimming in gunge. This had affected the mass air flow sensor and seemed to be the root of the problem. We have mechanically identicall 169 and 312 and note the 169 (our problem car) goes better although it produces gunge from the engine breather.
The bredth of the warnings and lights, plus the involvement of the steering system suggests this is a basic and fundamental issue. Sometimes
MES does not get right to teh bottom of such things but points to several areas of interest that are not involved. My suspicion would be its an earthing (or faulty wiring) issue, the main earth leads would be my first change / check, the battery would be my second suspect. You could check and clean the terminals at no cost and little effort, The third suspect would be the steering motor causing a short circuit and mucking up the ignition system in some odd way. Before delving into this a good check of the alternator out put would be a good move.
If its not electrical then some form of fuel starvation could be the cause.
Some checks with
MES would probably rule out quite a few of the above suggestions.
After years of bitter experience I now never rule out faulty replacement parts as a bunch of red herrings. This does sound like a diagnostic on the Fiat dealer system might be worth the cost. I do hope you get to the root cause sooner than laterand share your frustration.