The ornamental design for a diagnosticinstrument for a vehicle, as shown and described.
FIG. 1 is a front view of a diagnostic instrument for a vehicle, showing my new design;
FIG. 2 is a top plan view thereof;
FIG. 3 is a bottom plan view thereof;
FIG. 4 is a rear plan view thereof;
FIG. 5 is a left plan view thereof;
FIG. 6 is a right plan view thereof; and,
FIG. 7 is a perspective view thereof.
The broken lines are shown for the purpose of illustrating portions of the diagnostic instrument for a vehicle and forms no part of the claimed design.