Kia

I have a 2010 Chevy Impala my check engine light
is on I change the gas cap and I unplug the battery
and waited a while and plugged it back up the
check engine light went off for a couple of days
and then it came back on but I also noticed when
the check engine light is on I can't use my starter
on my mole control keypad but when the check
engine is off I can use my keypad starter I changed
the vent valve solenoid the check engine light went
off because the man cleared the code it stayed off
for about a two weeks and then it came back on
when this problem first occurred I took my car to
AutoZone so they can hook it up to the computer
they said that they got a code p0442 I don't know
what to do can someone please help me