The management system light has appeared on my OH Fiat Ducato van and has been acting weird.
First the light is intermittent - sometimes it comes on when starting, sometimes it doesn't. If it does come on then the van won't go over 30mph.
It has also started cutting out when slowing down. It restarts straight away but will do it several time throughout the journey - again this is only of the management light comes on.
The speedo also stopped working ages ago.
He took it to a guy with one of the thingies (sorry don't know the name) that will tell you the fault codes and got P0500 which we believe is the speedo, P1670 & P0191 which we think is to do with fuel.
We took it to the garage and he renewed the fuel filter and cleaned up the sensors but when he contacted Fiat they reckon that one of those codes could mean 1 of 4 things have gone wrong and that there's no way to tell which, you just have to replace each thing and see if it works but the prices Fiat charge for the parts is ridiculous. One of the parts alone was £615 + VAT
So far whatever the garage has done seems to have worked. Hubby says the van even feels different when he drives it but that was only yesterday. So I'm wondering if anyone else has experience with these faults and could suggest any other options if it happens again.

Thank you.

They are correct could be a lot of things, don't let them simply throw parts at it though, they'll probably start with a new hp pump, then throw an ecu at it. Very expensive quickly.

The free things you can check are the high pressure pump regulator connector and harness, check rail pressure sensor and harness wouldn't be surprised if you find the harness is damaged somewhere.