Can a DPE help you during a checkride?

The applicant is Pilot in Command during a checkride, and the DPE is really acting as a passenger and likewise can only help the applicant with stuff that a non-pilot passenger could do.  The DPE "passenger" could look for traffic, hold a chart or iPad or maybe grab something from the backseat.  However, the DPE "passenger" can't help with operation of aircraft systems, look up approach plates, teach/coach or help you fly the airplane. 

In the eyes of the FAA, DPEs are observers.  They are  observing your actions and how they comply with the ACS.  There are a few checkride exclusions that do happen.  For example, the DPE may fly the airplane when the applicant is putting on a view limiting device or maneuver the aircraft around traffic when you are under the hood but that's about it.

Anytime a DPE intervenes for safety of flight issues, the DPE has to issue a Notice of Disapproval.   For example, extending the Flaps above Vfe, trying to take-off with full flaps extended or has to recover the aircraft from a messed up maneuver.  The DPE also can not allow an applicant to break any regulations.  Examples would be,  flying into Class B, C, or D without authorization, allow you to bust VFR requirements or land without a clearance.