Problems ....

My left passager door does not lock. I checked the
fuse box and everything looks okay and the right
side works fine but the lock on the left will not
engage. Anyone have any ideas what the problem
could be.
Also my check engine light came on for the first
time today. But it only came on after the fuel cap
indicator came on. When the fuel cap indicator
came on I check on it right away, opened and
closed it tightly back. I went back to check to see if
the indicator was still there and it was. After driving
for a while the indicator came off and I thought I
was in the clear but no. A few hours later the check
engine light came on. What could be causing this?
Is it an easy fix?
Lastly after noticing the check engine light I had my
friend come over to plug in his OEM scanner to
read the codes. After it scanned it showed 3 issues
but when I tried to see the cold for each of them it
said N/A. Next I went to autozone to see if they
would know what to do. They also put in a scanner
and when it scanned the guy connected the
scanner to the computer but he said it did not show
anything. What does that mean? Please help!!