Yaris 1.3 Mk1 Airbag light flashing

[boyse7en]

My daughters 2004 Yaris is providing excellent transport, but with a looming MOT test i have got to sort out the one glitch.
The airbag light on the dash intermittently stays on, or comes back on, after the car is started. It then flashes for the duration of the journey. On restart it may or may not go out.

I've tried disconnecting the battery for a while. And I've unplugged, cleaned and re-connected the yellow plugs under both driver's and passenger seat.

I also tried my cheapo ELM327 code reader in the ODP port but no codes are present (I suspect specialist kit is required to access the airbag ECU).

Anything else i can do or is a trip to the Toyota dealership to have my pants pulled down on the cards?