The simplest check is also easy. Under the step is an amber light. WATCH the light and have someone OPEN and CLOSE the door with engine running. IF the light goes ON and OFF with the opening and closing, the wiring is OK and the probable failure is the step motor. SAME procedure with engine running and opening and closing the door. Tap(bang) on the step motor with a hammer. IF the step then functions the motor had a dead spot in the armature and needs replaced. It will probably work after you do this but WILL fail again. Doug