I had a couple of error codes some time ago 31 and 13.
I did a full check and turning on the air canceled 31 and dodgey contact for 13.
Removed error codes and then got the all clear codes 4green & 4red, but if I start the car next day and after driving code 31 is back which again is cleared by putting on the air.

My question is should error codes appear when the ECU is NOT in diagnostic mode as the screw is turned fully clockwise..