I have a 2003 Volvo s40 the check engine light was on when I bought the car there was codes that came up when I got home they only gave me 3 of them the codes are P0420, P0456, P0107. Im not sure what they mean or where I should start any advise would be great. Thanks

 

Check out this site:

Volvo P0456 OBD/DLC Error Code - Evaporative Emission System Leak Detected (very sm

It gives definitions of the codes and detailed info on causes, symtoms and possible solutions to them. On the right side of the page you can enter in the other codes to look at them too.

The only code I am familiar with is the P0420, my 2003 S40 has that one constantly. The car runs fine and I'm too cheap to pay for diagnostics... and most mechanics just tell you to replace the O2 sensor, which is expensive, and from what I have read usually does not solve the problem. They do sell a O2 extender which holds the O2 sensor further back from the exhaust stream and is supposed to cure reoccuring P0420 codes.