The check engine light means one of up to 11 systems has faulted enough to trip your MIL (malfunction indicator lamp). If you put and OBD II (ON-board diagnostics) reader on it, it will tell you which of hundreds of codes it might be. All cars made after 1996 are OBD II compliant (US at least, can't speak for other countries). While these codes shouldn't be ignored, they usually don't spell immediate impending doom for your car. Common problems are the fuel delivery or emmissions systems including catalytic converter. I bought myself an OBD II code reader on EBAY. These can read the codes and come with a book to tell you what the numbers mean. Knowing what the code is does not necessarily mean the answer as to what to repair is clear cut. I have an intermittent P0422 from my 01 V70 and sometimes it clears itself. But in looking it up on the Volvo Vadis system, there are several things to check for this code. OBD Readers cost $75/$125 if you're a smart internet shopper. I got a nice new one for $123 delivered with a hard carry case (Ebay). Also, I'd recommend getting yourself an owners manual just for reference. You can find them every day on EBAY for under $25. If you had an 01 V70, I actually have an extra complete manual set, but I think yours is 98. Good luck!
--
Don 01 V70 2.4T & 96 850S