I hope you mean the line in the shadow under the car :) If you do, are you using ray-traced shadows? If so, try using shadow mapped shadows. I Firefly rendered a picture using the sedan you have in your picture with my infinite light set to ray traced shadows, and had the problem you show. I then switched the shadow to shadow mapped and rendered again, and this time the shadow was solid underneath the sedan. My shadow intensity was set to .6 in both of my renders .