Technical Please! oh no I can not shut off my 3.0 Ducato

[bugsymike]

There is a special procedure for the x250 and newer models to disconnect / reconnect the battery to avoid the airbag module failure.

Good point, I am not familiar with later models.
Mind you if engine hasn't been switching off presumably the battery has to have been disconnected to kill it, which may account for any extra error codes OP mentioned.

 

[JOJOLYLE]

Some do and some don't,.
Regarding the relay I was thinking you could note the position and substitute for a different one, whilst also checking no signs of burning or corrosion around the socket.
A good diagnostic program used by Forum Members is MES which has a module activation facility to test some items and you run it from a window computer or tablet.
Sometimes it is possible to feel which relays become live clicking under your fingers as the battery is reconnected or whatever you have to do when testing.

When I shut the key off, the dashboard lights go off but the van keeps running.

NEW
With the key off, There is 5 volts on the load side of the Fuse22 (Ignition power) Back feed?

When fuse18 (30 NMC) is pulled The 5v goes away on load side of Fuse22 (Ignition power)

With the key in the off position, When fuse18 (30 NMC) is pulled, Engine shuts down, and the battery drain stops .

NMC??

 

[NeilDD]

Will a good electronic auto shop have access to the same kind of diagnostic equipment as a dealer. I love the challenge of a do it yourself but testing the ecu would be tough. If there was a stuck relay as in mentioned earlier. I would think that would show up in diagnostic. I would gladly pay 200 bucks to know what this problem is.

From what I know of US dealers, they will just swap out units at your cost until the fault is fixed.
I now it's a fair distance from you, but I would reach out to Ivan from Pine Hollow Auto Diagnostics, who may be able to help remotely, as he's in PA

 

[Bacchus]

Joined because this may help the OP or subsequent readers...

I bought a 2017 Ducato recently and came across an identical problem - the engine wouldn't stop even with the ignition key removed. My van is an ex-works van which had a second alternator fitted and connected to a device for providing 110V AC or 50V DC (for welding) so I think this is by design.

By accident, I discovered that taking the handbrake off killed the engine!

 

[the green vanper]

Yes, it is possible there was some specific equipment installed. On the bottom of the passenger's side B-pillar there's a third fusebox where normally all extra equipment should be connected.

As far as I remember it is described in the converters manual here:

x250: New Fiat Ducato. Conversion and fitting-out manual.

The original document prepared by Fiat Professionnal for builders / converters / upfitters dedicated for the Ducato x250 series.

www.fiatforum.com

There is no obligation to use this fusebox of course, but in Europe the professionnal converters consider it a good practice.