The CCD bus is the comunication system between all the cars or trucks controllers. It makes for alot less wiring. Its like if the speed sensor is picked up by the TCM (trans controller) it can be bussed out and every other controller on the car now knows the vehicle speed so you dont have to hard wire each controller that needs to know speed. Thats why alot of newer trucks may have the oil pressure sensor monitered by the PCM and then the oil pressure is bussed to the cluster and so on. Its best to put a DRB on it because if it says No Bus the DRB will tell you if its a short or a short to battery or an open or what ever because if the bus is down the DRB will usually say why its down but of course it wont tell you what the problem is. There are some comon problems but I have had all kind of weird bus problems over the years. Good luck , Ron