Can someone help me? I have this connection problem also. My S4 has analogue clock though and 551C ecu. I have wired new K-line straight from the ecu to OBD connector, but still most of the time it doesn't connect. Only very seldom it connects and I can log (very quickly before it loses its connection).
Ok, if you want to log with 551c you must do the following:
1) Disconnect the existing K-Line from the ECU.
2) Immo OFF the ECU
3) Run K-Line directly from ECU to OBDII connector.
Now it should work OK. I recommend using FAST init that way the clocks don't even try to wake up or do stupid stuff.