Примерно так:
Dim handle As Long, ch, sep, i
handle = FreeFile
Open "D:\Stuff\test.csv" For Input As handle
Do While Not EOF(handle)
ch = Input(handle, 1)
If Len(sep) = 0 Then
If ch = vbLf Or ch = vbCr Then sep = ch
Else
'vbCr + vbLf is a valid combination,
' otherwise it should be a single character....
If sep = vbCr And ch = vbLf Then sep = vbCrLf
Exit Do
End If
Loop
Close handle
If Len(sep) > 0 Then Debug.Print "Found line separator:"
For i = 1 To Len(sep)
Debug.Print Asc(Mid(sep, i, 1))
Next i