I have a 1997 A4 1.8T Automatic Transmission. The past week southern California has had a lot of rain, compared to what we are used to. Anyway, my car has been fine, till the last day of rain came. I put the gear selector in reverse but nothing happens, the box that surrounds the gear on the dash display doesnt even surround the R when in reverse, I play with it a little and it finally works. All other gears seem to work properly including the box that surrounds the gear indication on the display. So it seems when I drive in heavy soiled roadways, I have this problem with reverse. As of now it is not shifting into reverse and the check engine light has come on, and the display with the gear selection has every gear lit with a box around it now, I plan to check it today. My guess is that something electrical is getting wet. Any ideas or help is appreciated.

 

Not sure about your A4 but on the A6 the Transmission Control Module (TCM) is under the front passenger seat and issues have been reported after driving in the rain where rain got in the car because of drain blockage under the battery compartment (front right side of car).
Some had good luck with drying the TCM and putting it back on, so I would start there.

 

Well I checked my trouble codes. This is what I got; P0705-Trans Range Sensor Malfunction (PRNDL Input), the other code is, ;P1613 MIL Call-up Circuit open/short to B+. After I read the two codes I cleared them. Then I checked everything out and the boxes that surround the gear indicator went back to normal and I had reverse back again. I am pretty sure that something electrical got wet. Good thing the rain is gone for now. I plan to put my car up on the rack to look underneath it and make sure nothing is exposed that shouldnt be. I sure am glad that I have reverse back!