I have had a hand held fault code scanner/live data reader for a while and it will connect intermittently.

During a recent short period that I was able to connect my scanner I got my car remapped with no problems.

Since then I have been unable to connect.

I have recently purchased a VCDS cable and I am only able to connect to some of the controllers that I should be able to.

When testing the cable I get the following:

Port Status: OK
Interface: Found!
Type: Serial Pass-Through
Opto/Iso: No
Ross-Tech Design: No

Latency Test: Poor
2.6 3.0 9.4 (ms)

I can connect to controllers 3, 15, 46 & 56.
I cannot connect to 1, 17, 19 & 25 - for each one I get the message "No Response from Controller!".

K-Line to ground is 4V with ignition off and 11.5 with it turned on.
batt to ground is 12.3V.

The car has the standard radio and CD players fitted.

I have checked all the pins on the obd port and they are all secure.

Looks like a dodgy wire somewhere, any suggestions where to look?