take you car to a volvo dealer, its probably the abs control module. you are not alone, the 98-00 s/v/c70 series have been having the same problem, as well as the s80. you might also want to see if your local volvo dealer offers an extended warranty program, since the control modules are quite expensive. They are a very fast moving item in dealer's parts departments. you could try used, but you might get another one that is just as bad.