Hello,
it seems, that action “Add a force to an object” (All objects → Displacement) is partially broken. Moving on X axis is OK, but on Y axis doesn’t move at all.
Really? Can you send me an example file showing the issue?
Here it is.
Three files: two sprites and the project.
Project.zip (10.8 KB)
It is working for me 
Try to check the car position in the debugger (When you launch a preview, in scene tab ==> Debugger):
With the debugger ative, move the car with the key and check if the Y value changes 
Hm, my fault. My green ground is too big to define the move correctly. Thanks, Lizard-13, for the hint with debugger. Sorry for my false alarm.
