Workbooks.open("E:\sarath\PTMetrics\20131004\D8 L538-L550 16MY\D8 L538-L550_16MY_Powertrain Metrics_20131002.xlsm")
Or, in a more structured way...
Sub openwb()
Dim sPath As String, sFile As String
Dim wb As Workbook
sPath = "E:\sarath\PTMetrics\20131004\D8 L538-L550 16MY\"
sFile = sPath & "D8 L538-L550_16MY_Powertrain Metrics_20131002.xlsm"
Set wb = Workbooks.Open(sFile)
End Sub