This used to happen with my Passo, even while driving, the eps light suddenly turned on, and the steering got very hard, like Suzuki FX hard to turn. Got the CV joints changed and the Power Steering fluid changed and didn't give me a problem till I sold the car. This is usually a problem with the Inner/Outer CV joints, especially when their contacts get damaged due to wear and tear. Get them checked. Also get the alignment/wheel balancing checked.