Sable Door Keypad "5|6" button doesn't work

I have a 2000 Sable LS Premium and the 5|6 button(s) do not work. All other buttons illuminate when pressed. Unfortunately, my factory code starts with a 6 so I can not change the code to avoid this button. Any ideas on how to fix this? What connections should I be looking for that may be loose/broken? Please let me know. Thanks.