i use an ODBII reader i got off e-bay it works well, and clears any codes and lets you read them to work out what number it is, which is important. I also read some where that leaving the battery disconnected for a while then restarting the car will clear the codes. This however will not stop them reappearing, and also gives you no clues as to what error you are getting. If you know what the error was then a power reset is a fine way to get it cleared. I would urge caution in just clearing codes without working out what caused them.