F=Faulty Sensor=the computer that sense faulty???

I admit that Female and cars are not friendly to each other. I have no clue how to treat a car. My hu*****and really love your comments. He is another sexist on this female v. cars issue. Ok, back to original topic, the Description on Benz invoice is "Investigate Transmission fault. F coming up on dash board. Carry out short test. fault code for selecter module. £527.39". You see, not much information given. We are not convinced so we did not pay and change the sensor yet. Thank you.