When GPS sensors are no longer being utilized for position fixing while on the final segment of a GPS approach, the approach service level on the HSI will turn amber and the annunciation 'GPS NOT USED' will be displayed on the PFW. If the aircraft is at or beyond the FAF when the condition occurs, a system message to abort the approach will be generated. The CDI deviation bar is also removed from the HSI. Once the pilot acknowledges the abort message, the CDI deviation bar will reappear.