On Saturday the check engine light came on. This is a 2009 Ford Fusion. My daughter had just gotten gas so I figured it was gas cap related and did not panic. On Monday we had it checked at a car parts store and the codes were: B1318 P0841 P0410 and P049 The light had stayed on in spite of gas cap tightening and driving quite a few miles. Today (Tuesday) the light has gone off. Is is possible that all those codes were "false" or have cleared on their own? I have an appointment to get this checked but was wondering what your thoughts would be. This is a "new to us" used car that we bought on Saturday.
B1318 is low battery voltage
P0841 is a code for the transmission fluid pressure sensor (TFP)
P0410 is a code for the secondary air injection system (pump malfunction)
P049 is not a valid code, they are always Ptxxx. The first digit 't' (type) is always a 0 (generic) or a 1 (OEM specific). Perhaps you meant P0449 which is EVAP vent valve/solenoid.
NONE of these codes bears any relation to the gas cap, although the '4' series codes are emissions including the evaporative system (gas cap included). But P0449 is not a small or gross leak.
It sounds like the battery voltage got low, perhaps scrambled the ECU a bit. The fact that all codes cleared in a few drive cycles is a good indication that they were phantom.
Monitor to see if they come back, but they appear to be random phantoms and not even related to each other - unless the one "real" code was the battery voltage, and the other codes are a result of the ECU fainting for a moment.
Perhaps get the battery load tested to eliminate that possibility.