bikerick,
Yes, both Dell Series 9 ink cartridges need to be in the printer to work, with ink above the sensor.
Dell Series 9 ink cartridges have a sensor in them that cannot be reset. Article on refilling Dell ink cartridges.
Dell Series 9 ink cartridges can be purchased at Staples, Walmart or Dell's Website.
Black cartridge = black side(left side) Color cartridge = color side(right side)
Photo cartridge = black side(left side) Color cartridge = color side(right side)
It is possible to get a Dell Series 9 cartridge with a bad sensor. Contact the place of purchase for a replacement.
Rick