Shanks

Hi guys and thanks for any help in advance My 2012 a5 3.0 tdi went into the garage for a new steering rack no other issues. Car was returned and after a 20min drive luckily 80ft from home I got a gearbox fault ok to drive but no reverse gear. a scan of the codes revealed P17D700 Transmission Fluid pressure sensor/switch B range/performance. It’s back at the garage who seems to think it’s the mechatronic that has failed?