audi a6 2.5tdi 2001 auto gearbox problem

[brooksy4motion]

hi i have recently purchased a 2001 audi a6 2.5tdi estate with an automatic gearbox. it drives fine but every now and then when i put it in reverse it does not engage in gear. the gear display on the dashboard then flashes, (i can here a relay clicking dont know if this is the problem) it works fine in drive its just reverse that seems to be the problem. i have a receipt for a recent service on the gearbox so from reading other threads i dont think the oil needs changing. i havent had chance to have it code read yet and it doesnt do it all the time. does anyone have any ideas what could be the problem ?

[brooksy4motion]

just an update has this code read today and came up with:

17090 - p0706 transmission range sensor

18034 - p1626 mis message from transmission

does anyone have any ideas ?

[ametlib]

Not sure about this , but it seems like the tcu isn't communicating. I would have pulled the floor carpet and checked if the tcu is wet or have been wet, look for corroded connections