I got the VDC warnig as well, turned out I hadn't screwed things back together properly. Seem to remember it was that part that covers the relay (it seems to rotate) that measured the steering angle. In my case I had forgotten to put one screw in. Suggest you take it apart again and make sure its all in the right position.
Thanks for the advice Simon!
I did pull it all apart again and straightaway realised that the part-that-covers-the-relay (angle sensor) has a rotating centre black plastic sleeve, with a notch (key) that lines up with a peg on the clockspring. When I took it apart the first time, I assumed that central sleeve was for the self-cancelling of the indicators, but that is a separate, white plastic sleeve that has two notches to line up with two pegs on the clockspring... so although that was lined up, the sensor wasn't.
Unfortunately in the time between assembling the first and second times, I have managed to lose the correct position of the angle sensor sleeve - even though the notch is now lined up, I still have an error. Thinking about it, it must be one turn out (don't know which direction) so I could do this by trial-and-error, or hook it up to diagnosis to find the correct neutral position and reassemble.
Sadly, Alfadiag can't 'talk' to the ABS ECU (disappointing, but oh well), so I'm going to have to make a 90km round trip to a specialist tomorrow and use their equipment at some cost. Actually, the trial-and-error approach sounds like it may be faster - take off steering wheel (airbag still attached), turn sleeve one turn anticlockwise, refit wheel with nut finger-tight, drive down road and wait for warning (it takes a little while before the system decides the angle sensor is faulty - if you happen to brake during early manoevuring, there's the most amazing graunch as the system differentially-brakes the wheels as it sees the steering angle and assumes the car is in a big slide
If I still get the warning, I can try turning it two turns clockwise, etc. I hope there's no limit to the number of turns the encoder has, otherwise it's probably busted by now
I'll let you know how I get on.
I am guessing here, but I think the system decides that the angle sensor is faulty based on the speed of all four wheels - if the wheels are all about the same speed, but the angle sensor says the steering wheel is turned about one turn, then it flags the error. Until the system can read the wheels speeds in a straight line, the system behaves as not-faulty - hence the strange behaviour as it thinks there's one turn of steering lock wound on.
Also guessing - but I suggest that a wheel alignment (tracking adjustment) whenever necessary would be essential on VDC-equipped cars to ensure the steering wheel is always straight when driving straight. I suspect that if the steering wheel is off-centre (and let's face it, that's on many cars!), the VDC will not necessarily flag an error but may work incorrectly in certain braking situations, as it sees the steering wheel turned yet the car is not turning/yawing correspondingly. It might brake wheels incorrectly and make a dangerous situation worse instead of better. Just a guess, but based on what it 'sees', a logical guess, I hope you'll agree
I expect there is also a way to redefine the 'centre' position of the sensor, using diagnostic equipment. But it would be better to correct the wheel alignment instead (would have to be done very accurately with the steering wheel locked in place).
Hope this helps someone in the future... learn from my mistake... The angle sensor is NOT in the clockspring (several people seem to think it is). Get the angle sensor sleeve lined up as well as the indicator self-cancelling sleeve. The clockspring must, of course, go back on with the column in the same place as when the clockspring was removed (the clockspring has a limited number of turns in each direction, as it's a ribbon cable wound like the spring in a clock, hence the name).
Finally - if you know your car has a VDC fault, exercise caution in the period from when you start until the VDC Failure message appears... once the message appears, it's safe to drive (system is disabled because it 'knows' it's faulty), but until that message appears, the system 'believes' it isn't faulty and does weird things if there is a fault such as the steering angle sensor being one-turn out. I was caught out by a huge lurch in a carpark today (braking and turning, I stopped a lot quicker than I intended) - luckily didn't hit anything, but if someone had been following, there could have been minor collateral damage