Signal ground pin-lack thereof

Help please,

I'm fighting a complete refusal to connect to the OBD2 (MGZS 180, Mk2, 2004). It used to work with a cheap-o Bluetooth gubbins but nothing doing since footwell replacement surgery, either Pscan or other device.

I've got good plus volts at pin 16 and good ground at pin 4.

I learn that, from factory, there is no signal ground (pin 5) and this can cause failure to connect. Does Pscan cope with this internally or should I be jumping pin 4 to pin 5 to give it a fighting chance?

Thanks,
 

Pin 4 and 5 are already jumpered by the cable that comes with pscan, so if either of 4 and/or 5 are earthed then pscan is fine.
Does the green LED flash on the pscan interface when you plug it into the car?