Thanks Simmy and b1mcp for your replies I appreciate them.
However, the car has been on Vida as per my original post at a local Volvo specialist where I have the car serviced but no errors were shown, although they were not happy and don't know why, yet, there were no variations in voltage readings when the car's rear suspension loaded and unloaded.
They were supposed to get back to about it but to date I've not heard back from them, it looks like I'll have to go and rattle their cage, not something I like doing, but 100% right that somehow I need more definitive answers.
I have got OEM part numbers but prices I've seen for "genuine" Volvo sensors are obscene, hence my ask regarding alternative sensors and part numbers.
Thanks again guys for your input, I'll get to the bottom of it eventually, these newer Volvos are no where near as reliable as my old S40 or my old 440
Martyn