This is just informative, for search engines. DTC 01218 is the code for the Passenger side seat airbag.
Have a Audi 1999 A6 Quatro and had the dreaded Airbag Instrument panel light come on recently. I didn't uncover anything in google related to Audi cars, but did get lots of VW hits. I found this web page below:
which I followed (although the AUDI wiring had slightly different color - but there is only one YELLOW connector under the seat and that's what I cut out.
Soon as car was back together, I reset the error, and it stayed off (at least for today!)
Hope this helps someone else!