Judging by what you've described it sounds like it's the power steering control module. Either a loose connection/wiring fault.
With more information like what car model/year/engine code I could get you information of the location of the power steering control module.
Also I hope your multimeter has arrived because it is an indispensable tool when diagnosing wiring faults amongst other things.
I've attached a picture of how your multimeter should be setup to test for continuity (break in wiring). You place the black lead on any grounding point (somewhere metal on the car) then touch the wire with the tip of the red lead. It should make a beeping noise, if it does not then there is a fault with the wiring.
View attachment 133735
Sorry for the size.
If there is no wiring fault it could be the connector. Clean the connector with switch cleaner, just spray a moderate amount and connect/disconnect the connection multiple times.
If that fails then it will be the power steering control module.
On a side note, I would go to a different mechanic because the mechanic that said it drives fine and doesn't matter that there's a fault. It does matter just that it might not be a major fault. To me any car shouldn't have faults that are related to any function of the vehicle. Especially steering/engine/brake/airbags etc..