Hi James
Thanks - I just had a go at this and despite the beeps being random, all 4 sensors were clicking. Guess I need an auto-electrician!
BTW I just bought a gadget to plug in to the diagnostic socket. I went for one that connects by wifi and although it seems to pair with my laptop, I can't get it to actually connect properly. I've tried a couple of software options. Don't suppose you've tried this?