I had the similar VSC issues with my 05 GX. Bit of a story behind it. Not long after i bought the vehicle 2nd hand from the local automark dealer, i noticed a rattle from within the steering column. Took it to so-called steering and suspension specialists in PMB, who failed to sort it out, eventually purchased a new steering shaft, which required removal of the steering wheel. Thats when the problems with the VSC started. The Prados have a "yaw" sensor in the steering wheel, it sits behind the airbag. The yaw sensor is the device that figures out the car is in a skid, and applies the brakes selectively to prevent the skid (left front, right rear etc). If the steering wheel is removed from the shaft, and not replaced EXACTLY as it was previously aligned, the yaw sensor can go out of alignment. What i guess happens then is that as soon as the vehicle is in a particular situation , i.e. turning slightly, braking etc, the out of alignment yaw sensor thinks that the car is in an exaggerated skid, and starts applying the selective braking through the VSC system. Eventually, after many trips to the local Toyota dealer, whose mechanic had no clue (it even locked up the brakes when he was driving it), i parked it on a level piece of ground, wheels straight ahead, disconnected the battery, took off the steering wheel, re-aligned the yaw sensor with Top dead centre, then re-connected the battery. This then re-calibrates the yaw sensor. Since then i have had no more VSC problems. We know the VSC works as we often drive on a muddy road in summer, resulting in the odd bit of drift, which the VSC sorts out very quickly.
i dont know if this is the AA recommended way of sorting it out, but it worked for me.
