Finally had a chance to see what happened with my front parking sensors today.

Dropped the front bumper and removed the PDC Module which, interestingly was already a 931 module which wasn't released until after my car- obviously already been swapped once.

Thanks to BMW the plugs are keyed. Seems it's the blue plug for the front white for rear and black for power and comms.

I checked continuity on each wire (though I couldn't see any chafing)

Everything passed continuity check. As I didn't have any spare sensors I thought I was a bit stuck.

I figured I'd try swapping the blue and white shrouds (to defeat the keying) so I could plug the fronts into the rear circuit and vice versa. The shrouds pop off easily by moving a clip.

All four front sensors worked perfectly so it appears that the 'module1' circuit on the PDC module is the culprit.

Now to see how reasonable the LR Warranty people are- bet they still try to blame the wiring just so they can charge!

Anyhow hope this may be of some small use to someone.