It could mean many things; to find out you need the code it threw. '96 is the first year after the under-the-hood light/switch method to read the codes, so you will need a code reader. I bought a cheap Aquus that works great.

I think a place like Autozone will read the code for free. Once you have the code, you can search the internet for "Volvo DTC code" to find out what it means. People here can tell you how to troubleshoot a particular code once you have it.