A "mate" jet washed the engine bay and now the horn sounds when re-connecting the battery, lights come on, display shows a huge variety of error messages and car will not even turn over - grrrrrr
It hadnt hadn't run for a year but after a wash and having charged the battery it started first time, then the idiot we shall call Rick jet washed the cobwebs of the engine bay - der! That was the last time it started.

Left battery off all night and same problem
OBDI reader comes back blank
fuses look dry
ECU is dry
is there a master reset or anything else I can try??

If problems point to needing a new ECU, can i simply plug a new one in or is there more to it (as I suspect).

If you want to join me in insulting Rick :tosser: from Leicester, please do! :bang: :stupid:

Typical problem caused by water getting into the engine compartment fuse box, especially if the large black battery cover is missing. You need to dismantle the fuse box to dry it out.

There's a guide here: https://www.fiatforum.com/stilo-guides/313986-how-clean-dry-out-fuse-box-near-battery.html
.

You will have soaked your d2 connector under the fuse box behind the battery. Dry it with a hairdryer. Might have to dry other bits off too.

Might be called the d4 connector. Long time out of a stilo.

You can always rely on your mates to help you out in your hour of need

It'll be the fuse box, im sure.

I have had a similar scenario, just after hand washing. Do you own a battery cover?

My engine stayed running with the key out of the ignition and all sorts, scary stuff. Dried it out though and all ok