VW Golf, VR6, '98 - No computer communication

When I went for the emission test I was told that communication could not have been estalished between their equipment and my VW computer. I checked the plug (located right above the lighter) and there are five wires. I was told that two wires are for power, one for ground and two for communication. I checked two of the wires (red and grey/red) for power and looks like the power is in those two wiers. I was also told to check one of the wires for ground (white or yellow don't remeber exactly) but I could not find it. Could this be the problem that the ground wire got disconnected or broken? If so, what is the ground wire connected to and how can I check it?

thye problably used a shitty scan tool. Most scanners (other than vw tools and big brand name , ex snap on, mac) wont even access vw computers