Ah, the cold weather has arrived! You have found one of Volvo's common problems. It is likely that your air pump, an electric pump that lies under your battery tray, has failed. This pump comes on during a cold start and runs for a short (less than 2 minute) time to pump air into your exhaust asystem to help heat up the catalytic converter faster. It only is invoked at colder outside temps and sometimes after long highway runs. There is a flaw that allows moisture to buildup in the pump and freeze it solid or cause the bearings to rust and seize. The cure is to replace the pump and a checkvalve. Cost is about $400 or so at a dealer. This won't last forever either. Expect to replace this pump every few years, even if your checkvalve doesn't fail. The design is poor. Newer models don't have tihs pump I am told.

Although you have reset the check engine light, it will come on again as the slef check system finds the failed pump. In many states you will not be able to pass an emmission inspection because of this problem. An error code will get stored and the inspection software will not get a ready state. You have to spend the bucks and get it fixed.