To do this tutorial you must have a great understanding of the pen tool, il will not go throu each individual stage and walk you throu every little thing i do, you will be left to your own devices, but will help you the best i can.
Open up the image you want to cartoon, create a new layer and label it “lines” now select the “pen tool” and start drawing around the car do little bits at a time, make sure you get every little detail. when you’ve finished you should have something like this.
Create a new layer and name it “base color” and fill your car with a light greyish color.
Create a new layer and name it “shadows” then select your “pen tool” and select all the shadows then use fill path, fill it with the color black (to see where the shadows should be just hide your base color layer).
Create another layer and name it “highlights” then select your “pen tool” and select all the highlights color them white.
Now if you unhide any hidden layers you should have something like this.
Do the same for your lights, windows, exhausts, tyres, shadows etc… make sure you put them all on seperate layers, eventually you should have something like this.
Copy the “base color” layer and put it under the “highlight” layer but above “shadows” layer. Color the copy of “base color” the color that you want the car to be. By having the color on a separate layer, you can change it later and it won’t affect the shading at all. also play with the opacity of “highlight”, “base color” & “shadows” until you get a look you like this.