Rear speakers

Hi i have a Pioneer DEH-s5000bt stereo and everything was working just fine, until one day i turn on the stereo and noticed that only my front speakers were playing and not my rear ones too. I went into the audio setting and checked the crossover and it only said front and when ever all 4 speakers were playing i could see front and rear on the crossover but now i only see front. If you know what might be the problem plz let me know. Thanks