I'm not aware of a transmission warning light on the dash. I looked in my owners manual and non is listed. The check engine light is located immediately to the right of the trip reset button. If you're sure the gas cap is ok, then I would check all the hoses associated with the evaporative system.
There will be a hose from the tank to the charcoal canister, from there to the engine compartment where the solenoid operated purge valve is located. During the purge cycle, the solenoid is pulsed rapidly, switching the charcoal canister to the intake manifold where the fumes are burned. When the purge cycle is going on you will hear a popping or clicking noise coming from behind the glove box. The purging is determined by the the main computer based on driving conditions, such as miles,speed, number of starts,etc. The purging valve is located in the engine compartment, close to the firewall, on the passenger side.
HTH.........Stan