Partner steering vibration spongy handling

I also drive a Peugeot Partner, although a newer model. Your symptoms do sound concerning. Vibrating steering, spongy handling, and increased steering effort definitely point to a problem within the steering system. The error code makes it more specific. It could be an electrical fault in the steering system's cable or plug connection. Have you checked those?

Thanks for the advice! What exactly do you mean by 'electrical fault in the cable or plug connection'? Where should I be looking?

By that, I mean that a loose or corroded connection at any of the plugs associated with the electric steering components could cause intermittent issues. However, fiddling with electric steering can be risky. Considering the error code and the symptoms you're experiencing, taking it to a workshop for a proper diagnosis is advisable. A faulty connection is a common cause for issues with the steering, and it can be addressed rather quickly.

OK, thanks. I went to a workshop. Turns out it was a defective cable connection, just like you said! They sorted it out for 95€, which I think is reasonable. Steering is back to normal now!