06 Mountaineer wrench light comes on and stays on (unless reset) only after getting on the highway. It does it every time we get on highway but not if we do extended driving on back roads. Previously we had the transmission rebuilt due to towing with overdrive on. Store bought code reader does not pick up any codes. Car drives fine but overdrive disengaged light does not come on. when over riding over drive, we can see change in RPM consistent with button working but no light.

thoughts?