Chrysler Repair: 300M Check Engine light, free diagnosis, gas cap

Question
My 2001 300M check engine light came on.  Autozone does a free diagnosis and told me it was a worn out gas cap.  I bought a new one, the light is still on.  The guy said it'd take 50 engine starts with the problem fixed before the light would go off.  Is this correct?  Or do I need it reset by a tool?  Or is it possibly something else, not the gas cap?

Answer
Hi Kevin,
You can cancel the old code by disconnecting the battery for a few minutes. Then see whether the light comes on again after you reconnect the battery and drive it for a bit. If it does, get another readout and ask for the code number this time and let me know what it is and we'll go from there.