Hum.
Note that basically there are two sides to a Controller-Transmitter The charage and the RF { signal sending side } One can work and the other can fail.
Do you have a friend with a controller using the same freq? Can he controll your car?
Ok if you want to do this at your own risk and could, may, whatever fry any warrenty you have, you could try the following. IE your on your own!
Use a screwdriver to open the case and inspect the board for any cracks, cold solder joints, no solder joints, shorted solder connections. It usualy a single sided pc board. Best to use a mag lamp but if your eyes are young you can usualy see if something is wrong. There are many pictures of both side of the transmiter board that you could use as a reference. You will need a small prob like a screwdriver or better yet somthing plastic that you can tap, move, shift whaterver a solder joint. You do this unpowered.
What you are looking for:
A blob of solder like a round ball.
A blob of solder linking two point that should not be connected.
A patch of copper with a wire sticking up through it minus solder.
A part that when tug slightly come loose. But looks connected.
Cracked or broken part.
On the foil non-componet side there is a crack. Hold to light.
Missing parts.
If you have experence with a voltmeter or better a Oscope grab a copy of the circuit diagram. Start at the TX2 IC. Its the only IC there. See if its getting voltage. There is a transmit signal pin that I think keys the osc. See if it changes state. If not, then suspect the TX2 chip. If its changing state. Then go after the osc. Then the Buffer-Driver. If you have a Field strength meter do you see anything being transmited. Or a receiver that can receive that frequency do you hear anything when you push the buttons?
Good luck!