Electro-mechanical Power Steering

I got a yellow warning light indicating "partial failure of electro-mechanical power steering", although no actual fault apparent i.e nochange in steering effort that I could detect. Garage (independent not SKODA ) diagnosed a faulty component ( torque sensor? ) and changed this but yellow light came back the following day! They now say with "updated software" that I need a new powers steering unit at a cost of £550 plus labour plus VAT. Major bill.

After driving for several weeks and still not detecting any change in steering characteristics I am reluctant to authorise this major expenditure if the fault could be something small which they have missed. Any ideas / suggestions would be welcome.

Is this a known fault with the latest type of power steering?

Is it really entirely electro-mechanical now or electro-hudraulic?