Aubrain

It sounds to me like you've got the keybind set to something other than Shift.
In your keybinding settings, look under the "Movement" section and see what key "Sprint" is set to. That's the key that will blip a car for you to stop when you're in your police car. You can change that to Shift if you'd like, or leave it however you have it set and simply use that key to blip vehicles.

So I managed to get a much better quality build for a few less dollars.