I'm after some guidance regarding potential parking sensor fault causes.

The parking sensors on my XFR have stopped working, and the 'parking system fault' along with a long beep happens every time I start the car. It's showing 3 codes for faults on inner right, inner left and outer left front sensors (B1B38,40 and 42). Before the system decided to not work permanently, I got an intermittent fault, which has made me think that it's a dodgy connection somewhere: the workshop manual suggests that the front sensors are connected to the control module with the outer right nearest the module, which makes me think it could be a wiring fault, but I'm not sure! Any thoughts as to the likelihood that my diagnostic is correct (vs 3/4 front sensors being faulty)?

If there is a wiring fault, what's the best way to narrow it down to a particular stretch of wire? I have a multimeter but very little electrical competence, so I'd like to get as many ideas as possible before I go taking the front bumper cover off at the weekend.

 

cheeky bump - any advice r.e. troubleshooting parking sensor faults would be appreciated!