GE Microwave JES1334WD Code -P3-

Question

GE Microwave JES1334WD started showing a code -P3- after use this morning. Unplugged for 10 minutes then plugged in. All lights on panel came on then it beeped loudly several times and showed code -P3- again. Owner's manual does not show any codes. The door is firmly closed. The 3-prong plug is in a 3-hole receptacle; no 3-prong to 2-prong adapter is being used. When the panel first lights up there is a CODE on the top line of items. How do you get into the codes? What does a -P3- mean? Thanks for your help. BJ