"Rear brake sensor needs replacing" What is this?

I have seen a volvo v70 for sale, it says rear brake sensor could do
with replacing and rear disks soon. What is this rear brake sensor,
and is it costly to replace? Not some kind of expensive ABS fault is
it?

How much/labour to fix the sensor? And the disks? I am in the UK

 

Could be, you have not mad it very clear what sensor you mean. It could be
the pad wear indicator or the ABS pick up both jump to mind. The former
being cheap as chips, the latter being a bit dearer. As I recall £50 - £100
each. Is the ABS light behaving normally?
Is a light on the dash telling you you need brake pads?
Do you need new brake pads but have no warning light?

 

The ABS control unit is faulty. An easy bolt on. See:

http://home.earthlink.net/~vicrocha/Volvo_Parts/Volvo_V70_ABS.htm

for information; diagnosis and repair.

Bob