2012 R350 BlueTec, this year the steering wheel became a lot more heavier than before. There is no code, no message, nothing can see.
I had the same problem with a 07 X5 4.8i. Can't find anything wrong obviously. Lubricated all joins, etc. Didn't change.
Is the motor become weak? Where shall I look into?

Thanks
Jirong

 

Is it heavy for the whole 360 degrees of the turns or just for part?

 

whole 360 degrees, thanks for helping. I am wondering if the electric motor gets weaker over the time.

 

The power steering is driven by a pump on the engine. Typically this pump going bad is the reason for hard steering. There can also be air in the system, but if there was air in the system it probably damaged your pump. There's also the possibility of the steering rack wearing out.