Help with Codes

I brought my 2002 Denali XL to a shop to have it scanned, since my "service ride control light has come on. Here's the codes that came up:

C0281 Brake Light Switch
C0660 Level Control Exhaust Valve Circuit Malfunction
C0870 Device Voltage Reference Output 1 Circuit Malfunction
C0495 EVO Tracking Error
C0711 Unknown Trouble Code Description. Please see your factory service guides for more information.
U1300 Class 2 Communication Circuit Short to Ground



I'm sure C0281 is there because my 3rd brake light is out. I know C0660 has to due with the exhaust valve on the ride control compressor.

I need help figuring out what the others are for, and could they be related (i.e. is U1300 there because the brake light is out?)

Thanks for any information or help that you can give!

The best thing you can do when you buy a car is get a Haynes or Chilton manual for about $19 or you can get one on eBay for $5 and it has all of that information in it. Also, get a code reader from auto parts stoe for about $40 and you can erase your own codes (now they are stopping to erase codes). Finally, goggle the code and it will sometimes tell you what a fiox is - for example, most times a PO445 is fuel related, all you need to do is buy a new gas cap!