E46 reversing sensors question

[coopedup]

Morning all,
A quick question from a mechanical luddite, when I put my car into reverse it chimes when the passenger wing mirror goes down to see the curb but the reversing sensors appear to be M.I.A., where do I start, could it be a fuse or something more costly?
Many thanks in advance

[Smuler]

I'd check each sensor, put keys in, turn to position 2 (but don't start engine) and then put car in reverse and get someone to put their ear by each sensor. They will hear a clicking noise if each sensor is working. I guess if all 4 do not click, then checking fuse box makes sense. I believe you can access via glove compartment and diagram sheet is very clear.