sorry cant actualy help but our local dealer contacted vauxhall technical as they could not fix similar problem on our zafira and they eventualy admitted a design fault, it does however at least for the moment seem to have cured itself has has only gone off once in last year. fingers crossed that is!, the other possibility we were told is a spider in the works! may sound daft but you could try spraying as much as possible with insecticide in and around vehicle and leaving doors shut for a couple of hours worth a try anyway.
tim, July 2007