I have a 2002 Mercury Mountaineer. Started with the steering wheel controls working wrong, windows won't go down, check engine light is on, says door ajar when it's not, heated seats won't heat, now it's saying check transmission.
Have the trouble codes checked, manufacturer specific as well as generic codes. See if the code points in any particular direction? If you want to test one system start with the power windows, check voltage and ground at wiring harness, hinge side of door.