Hi I thought I would post this as it may be of some help to other users. I have recently had many issues with the "airbag failure, stop engine"

I had a VAG cable to connect to the engine ECU via the free downloadable programme from FIATECUSCAN.com. This does not connect to the airbag ECU as that is on PIN 3 of the cable and from what I read the VAG cable only reads PIN 7. So I followed the guide to amend the cable and soldered PIN 3 and PIN 7 to the original output via a microswitch.

After connecting my laptop to the Airbag ECU. I had six airbag faults in the memory. I was not sure which connectors in the car applied to "middle passenger airbag" or "curtain airbag" and so on.

All of my problems were with the passenger side so I disconnected all the connectors I could find.
The yellow connector above the little flap in the glove box.
The orange connectors above the rear suspension accessible under the little cubbyholes in the boot.
The orange, white and grey connectors under the passenger seat.
I also removed the whole passenger seat as I could feel folds and crinkles in the OCS mat under the upholstery.

I followed Deckchairs guide to replace the OCS in order to get to my existing OCS. Rather useless glue Fiat use to stick it to the foam. Mine had moved and become folded onto itself so I straightened it out.

I ran the airbag ECU and found 9 faults. I went through plugging the connectors back together (after giving them a spray with contact cleaner) and seeing which faults disappeared to come up with the following guide.

Yellow connector in glovebox - cleared -
09 Passenger squib circuit error 98
0A Middle passenger airbag squib 2nd stage error 114

Rear driver's side orange connector - cleared -
21 Curtain airbag squib (driver) error 210

Rear passenger's side orange connector - cleared -
20 Curtain airbag squib (passenger) error 210

White connector under passengers seat - cleared -
1D Front passenger's selt belt switch error 202

Orange connector under passengers seat - cleared -
0F Side airbag passenger error 203

Grey connector under passenger seat - cleared -
32 Front passenger weight sensor error 203.

hope this helps someone in their diagnosis of connection issues

2 years later and someone needs the info. These type of posts help endless people.