Can't make two loops work

Hello, here's my problem. I've got codes in column D that may show up more than once. On column A I've got a list of all available codes, and in column B the corresponding address. I want my macro to automatically replace each code in column D for its corresponding address.


Sub CambiarCodigos()
Dim iRow As Long
Dim jRow As Long
iRow = 3
jRow = 3
Do Until IsEmpty(Cells(iRow, "D"))
Do Until IsEmpty(Cells(jRow, "A")) 'works OK
Cells(iRow, "D") = Replace(Cells(iRow, "D"), Cells(jRow, "A"), Cells(jRow, "B")) 'works OK
jRow = jRow + 1 'works OK
Loop 'works OK
iRow = iRow + 1
Loop

End Sub

I really hope you can help!