just purchased this auto.....has cd changer in trunk on 2002 Mercedes-Benz SLK320

mecedes oem changer. when I hit CD button, screen reads
NO CD CHANGER........ took cd cartridge out and placed back in 4x.Still reads no cd changer.Any idea what to do for a FIX?

Asked by for the 2002 Mercedes-Benz SLK320