I haven't got an Astra but if a yellow warning light comes on it generally indicates that there is a fault if it stays on all the time.
If the airbag light stays on in our 2008 VW Golf it indicates a fault. Once it was the wiring under the drivers seat, the second time it was a crash sensor in the front passenger door. It needed plugging in to their computer to identify the fault each time.
ChicksFan, November 2012
