Not flashing at all is the relay/hazard switch. Pull the radio out, reach in and push the relay toward the seat to pop it out. Flashing fast is usually a front bulb socket problem. There was a recall on these. The original bulb/socket had a crappy plug in bulb, and the socket terminals would get hot and burn. The replacement bulb/socket had a traditional 1157 type bulb, and are very reliable. Call your local dealer and ask them to run a VIN report and check for outstanding recalls. Other possible recalls for your car include headlight switch, headlight bulbs/wiring adapters, passenger airbag ground, mass airflow sensor conector, A/C compressor, and wiper arm stop lugs. Not all cars got all recalls. Volvo database will have the info, or the N.T.S.B.