Set the **** like this:
Assuming it looks like that. Make sure you have it on the direct current side set to 20(since it'* a 12-14.4volt system).
If you're still not sure, we'll try to be a little more descript.
You can test by starting the car and putting the positive cable on the positive battery terminal, and the negative cable on any bare metal on the body, or the negative terminal. You should see a reading over 12.x volts. You can check the voltage of the battery with the car off, and then test it with it on to see the difference if you want to reassure yourself.
I'm afraid I can't answer the questions regarding the CEL codes....