It might be that your pcv valve is plugged or the egr valve is sticking.
It would be very rare for a P1684 code to turn the light on.
parking brake on.
Failed fan motor, relay, wiring, fuse, computer.
Well a lot of them have the same engines & transmissions; but if you have a lot of people you'll be driving around, you'd want the grand caravan...The only difference is the length. I would go with the standard size, it'll probably get better gas mileage and cause less wear on the transmission & engine.
Low trans fluid, or internal trans failure.
Leave it turned off.... doh
The most likely cause would be low fluid level.
It can cause it to only have second and reverse gears.
Either the solenoid pack or most likely the torque converter itself.
it could either be a bad beattery or a bad starter
A bad cam or crank sensor can cause a no start, but the engine will still crank or turn over.
The light will reset itself when the cause of the code has been repaired.