Two Questions

My parents have a 2001 Malibu, gas cap was left off, therefore the check engine light came on. The owner's manual stated vehicle might need drove a short distance before light would go off, but the engine light won't go out.

Same vehicle apparently had keyless entry which we didn't get when buying it used, and door locks, security system always causing problems because everytime door locks are flipped it resets the code and there are several different codes that can be set. Advice????