control system 109 further includes a plurality of relatively autonomous controllers or operators may include local data processing and programming and are typically supplied by the manufacturer of the controlled component these controllers include the transmission controller 140 a the engine controller 115 and the gauge controller 117 there may also be generic programmable controllers which may be used to carry out operator defined tasks though they are not limited to such functions the assignee of the present application markets generic controllers for controller area network applications termed remote power modules which can be readily programmed from an external diagnostic port 136 or by the electrical system controller 111 in response to particular hardware attached to the remote power module the common data bus 110 is typically a serial data link 110 constructed as a twisted pair cable it is typically externally accessible via a diagnostic port 136 although the autonomous controllers handle many functions locally and may be capable of functioning without reference to esc 111 they exchange data with esc 111 and can receive operational direction from esc 111 over the data bus 110 bus 110 typically operates in accord with a protocol such as the society of automotive engineers sae j1939 protocol relating to controller area networks can in an sae j1939 compliant can data buses may be private or public a system.