Jay the First

Driving through heavy storm water 2ft in places, my viano died. In the morning I went back to it and it started in limp mode. I inspected it at home and got PO 715. I looked all over and found that the rear right ABS sensor was loose and damaged so i ordered that. As it was going to take a week to arrive I decided to do the Control plate in the bottom of the gearbox and oil and filter change kit. I checked the solenoids by putting 12v across them they all click. (Still waiting for a dipstick to arrive), so i put in the same amount of correct ATF plus half a liter for the moment. I also replaced the 13 pin plug and oil seals to be safe, there was no leak.
Rear sensor arrived today so i fitted that and limped to a Auto Electrician who has a good computer to clear the fault. No fault showing in main ECU but cleared it in TCU, but the PO715 fault keeps coming back "stored in N15/3 Electronic Transmission Control (ETC/EGS) module (PO715)
Any ideas where i should look next?
Also I cant find the transmission computer box does anybody know where it is on a Viano? the main computer is up in the fuse box.
Im not a full mechanic but used to drive heavy truck wreckers so i can find my way about. Sort of.
Thanks in advance.