The D4 light keeps blinking, Why?

Have the check engine scanned for the codes, and it should lead you to the fault. Post the codes and we will try to help with your issue.

NOT code reader at auto zone. 'D4' blinking means there is a trouble code(s) stored in trans control module. IF the check engine light came on AFTER the D4 light blinking began , then the only code you'll get out of a generic code reader is a P0700 , which just means a trans code is stored in the TCM. Post the trans codes and we can definitly help.

AGREE WITH NUMBER 2