I've working my way through the driver's manual for the XF and one minor item has confused me. There is supposed to be a sensor to detect that there is someone sitting in the passenger seat. If there is then the passenger airbag is active and everything is normal. If there isn't then there is supposed to be an illuminated indicator advising me than thr passenger side airbag has been turned off. This does not illuminate when there is nobody in the passenger seat. Is this a system setting?