I have Mercedes E350 2009. When I hold steering wheel straight, car drives straight. When I lift my hands off, car and steering wheel tend to turn right. What could be the reason here?
There are several things that can cause this - the simplest being the road itself! If you are on a cambered road, the car will want to pull towards the edge of the road...
Presuming it's a stronger pull than that, your next suspect is the tracking (wheel alignment) - if this is out it will cause it to pull. Most decent tyre fitters will be able to check this for you, and adjust it for a fee. It's worth doing this every so often anyway, e.g. each time you fit new tyres.
If that doesn't fix it, check your brakes - if one is rubbing, it will slow the car on that side, and so cause it to pull across. After a drive, bring the back of your hand towards the centre of each wheel - make sure the right hand one isn't hotter than the left.
You can also have problems with electric power steering, but I don't think Mercedes use that...
Your vehicle should be checked over by a Mercedes mechanic. The front suspension and the rear suspension are both adjustable and can also be susceptable to damage, bushes, tie rods, ball joints, wheel rims, tyres. In many instances the correct service tools are required to carry out an effective repair or adjustment. There are several versions of the 2009 E350 and some do have electric PAS. It should be borne in mind that a small amount of control applied to the steering wheel would be covering a much larger effort at the steering components. The steering also requires setting with a scanner, as it ties in with the ABS.