The body bus (K-bus) in the E39 is, in the same way as the diagnosis bus (D-bus), the instrument bus (I-bus) and the peripheral bus (P-bus), a serial data link between control units.
The control units connected exchange information via the K-bus, e.g. sensor values or lamp status.
The following control units can be connected to the K-bus:
All functions of the automatic heating and air conditioning control system (IHKA) are operated by pushbuttons. Temperature, air flow and air distribution in the heating control system (IHR) are adjusted by means of thumb wheels.
The automatic headlight vertical aim control (LWR) is only installed in conjunction with xenon headlights. Unlike the manual headlight vertical aim control system, it features no control for vertical adjustment of the headlights.
The functional principle of the K-bus is comparable to that of a telephone conference circuit. All participants are interconnected via the K-bus. Every participant can both receive and transmit messages on the K-bus.
The K-bus is designed as a single-wire bus system, i.e. the K-bus is a cable which is used to transmit and receive messages.
The high data transfer rate on the K-bus (approx. 10,000 bit/sec) enables distribution of messages between the control units virtually with practically no lag.
DIS diagnosis telegrams are sent to the electronic instrument cluster via the diagnosis bus (D-bus). From the electronic instrument cluster (IKE), the diagnosis telegrams are routed to K-bus control units. The response telegrams of the K-bus control units are also sent back via the IKE to the DIS.