just put a Y8 motor and Auto Tranny in my 98 Civic EX. got it going and the D4 indicator is flashing. Also the tranny seems to hold 2nd gear for along time, then it slips going into 4th. once it takes the gear it runs fine.
I did put Honda fluid in the tranny, ZC1 I think it is. is it a bad sensor? also I cant tell if I may have over filled the trans, do you check it while it is running like most other cars? when I check the dipstick while running it is completely covered. when its not running it is right at full.
any help would be great. Thanks

 

flashing D light means you have a stored AT code...pull it and see what it is.