My check transmission light comes on when I'm using a/c. This doesn't happen when I'm driving with out a/c off.
This is on a 2005 Ford five hundred sel

 

Sometimes a poor ground in a circuit will cause those electrons to find another path to ground and this time they could be using the trans light circuit.

You might start with checking all ground connections to sheet metal making sure they are clean underneath and tight.

 

are you talking about the wrench light? my 2007 sel likes to surge from a stop causing the check engine and the wrench light to come on and it drives poorly. thought i had a big problem at first but all i have to do is shut the engine off and everything is back to normal. been going on for 3 years now and haven't figured it out yet. this 500 does some weird things but has 151000 miles on it and done pretty good. my problem sounds different from yours i know. did you figure it out yet?

 

I have the wrench light plus check transmission. Car runs fine.i can shut off the car and restart it and message disappear.
there's is one code in the system for the transmission. My problem is a electrical a bad ground.

 

Please keep in mind a code does not always tell you what is wrong , it just tells you what system is having a problem and it is up to a tech to chase down the cause..