Hi,

Terminal 30 relay J317 in E box under battery, supplies voltage to many fuses, it is switched on (neg) by engine control unit.
in the diagnostic "IDE00019 Voltage terminal 30 4.9 V " - terminal 30 relay switches battery voltage, should be more than 4.9V, but that 4.9V is being read from where ? If you can measure at connector T16m pin 15 you will get a better idea. (engine running).
You could check for any nearby earth connection as well, the earth terminal at the T16m is pin 16 as far as I can make out, that should be a brown wire.
My notes are a bit limited. I don't have diagram for the J329 Terminal 15 relay, which is under the dash fuses, but usually all engine controls are in the Ebox as I remember.