I don't know but maybe we can figure it out . . . is "PSCM" = Power Steering Control Module? How is that tied in to the Advancetrac system?
I don't know why the Advancetrac would be tied in to the steering. I'm pretty sure it only uses the same sensors that the ABS uses; they sense wheel speed, compare the four wheels, and activate the system is something is out of whack (one wheel turning at too big a difference in rate from the others). So I would check that first -- make sure all four sensors are clean, the wires are intact, etc.
Generally tuners are very reluctant to mess with safety systems for fear of liability, but maybe you can get someone to do it . . . I assume you are in Great Britain, maybe someone there would do it?