on side of the ROAD

David, is your transmission the 3060?..Have you pushed both arrow keys at the same time to see if you have any additional codes. If the 66 is a serial communication fault.. The likely you are talking about communication between engine and transmission relative to throttle position..Chances are good its a connector issue... There are a lot of references to this issue on the net if you have reliable access.

Here is a link that has some specifics.. http://www.schoolbusfleet.com/forum/topic.asp?TOPIC_ID=13070