Actually, you can use the onboard diagnostic box to check the crank position sensor is working- although beware they can work intermittently when they’re failing.
Use this guide:
https://www.volvoclub.org.uk/faq/EngineOBDCodes.html
And this thread has useful photos:
https://www.volvoforums.org.uk/showthread.php?t=122391
Cheers