Citroen C4 Grand Picasso 2015 MK2 Brake Fault

[Charris13]

Hi all
I've jumped on this thread rather than start a new one as it's the same problem I'm having.
Citroen Grand Picasso 2017 diesel.
Getting the orange warnings for ABS, ESP, Handbrake, hillstart etc. I've run an icarsoft reader which has thrown up codes C1387 coherance and C0037 rear left sensor which remains even after a new sensor has been fitted.
My husband has checked the wires but can't find any breaks from the wheel arch area etc

How does he find where the wires run to inside the car? Can't see how to remove the back seats etc so any help appreciated.
Many thanks