Most codes will clear themselves after so many on/off cycles of the engine. Some may be as little as three or as many as 40 (so I'm told). When I got the CEL for leaving my MAF unplugged I wasn't going to wait for the CEL to clear itself, so I cleared the code. I have a scanner of my own to do that, but for most people pulling fuses or disconnecting the battery for a short time will suffice. On both of my Duratecs, pulling fuses 4 and 11 do the trick.
