Mirror of a sketch

To mirror in a sketch you need to have a construction line in the sketch

Maha,

It's not a 3D, it's on the Front Plane. You are trying to Mirror a Partline Surface, not a sketch. Having said that, not sure why it's cutting a hole. Someone with more experience might be able to shed some light on that.

If you open the sketch for the part line & mirror your geometry in there about construction line on the origin, then you should be able to edit your partline feature & select the second surface on the opposite side & then it should work.

Of course, you could just model half the car & mirror the solid body at the end.....assuming it's symetrical.

Not sure why your bumper is shelled out and the part i downloaded isn't. Also it did not open with the hole cut out on the right side of the car body like you have shown, just the split line on the left side of the body. But this is a simple Extrude cut with the sketch you had in the split line mirrored to the other side. Its cut depth is 800mm so that it passes through to the fender wells.