P1536 code? Also...

I just had azo pull codes and it came up with p1536, any clue what that may be?

Also, probably not related, but I put on new air springs a short time ago and sometimes the truck doesn't level itself off and there's a slight lean to it even if it sat overnight.  The main reason I had the codes checked was to see if I needed a new height sensor, but instead only got the p1536.

Any thought?  Thanks