Technical Description: VR-bus: Notes

The VR-bus (Valve and Relay bus)is a single -lead bus communications link through which the STC control module controls one relay for each window lift, one relay for the fifth bow latch motor and the four electromagnetic hydraulic valves.

A bus is understood to be the leads with which information is sent digitally and serially. Digital means that the voltage difference between the leads has only two values, in this case roughly 0 V and 5 V. The information is coded so that different combinations of 0 V and 5 V pulses have different meanings.

Serial means that information is sent in "packets" that are sent in succession at a rate of 15 000 bytes/second.

Fig 1: Identifying VR-Bus Control Module Components

Courtesy of SAAB-SCANIA OF AMERICA, INC.

Fig 2: VR-Bus Communication Connection Diagram

Courtesy of SAAB-SCANIA OF AMERICA, INC.

All information sent out on a bus by a control module is available to all other control modules connected to the bus. Each component has a programmed name, e.g. "Front Left Window". The information sent on the bus is used only by the affected component. When ordered as spare parts, these components are not programmed on delivery and consequently must be programmed with the diagnostic tool.

The control modules send out information on the bus at regular intervals. Information is also transmitted by the control module whenever the information changes.

VR bus communication takes place on pin 14.