Body bus (K-bus)

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 connected control units exchange information via the K-bus, e.g. sensor values or lamp status.

Design and function of the K-bus

The following control units can be connected to the K-bus:

• LWR: Headlight vertical aim control
  
• CDC: Compact disc changer
  
• DSP: Digital sound processor amplifier
  
• ZKE3: General module of ZKE3
  
• IHKA/IHKR: Automatic climate control or heating control
  
• KOM: Instrument Cluster (Basic)
  
• IRIS: Integrated radio information system
  
• EHC: Electronic level control
  
• LCM: Light check-control module, installed as of 9/95
  In the light check-control module, the functions of the light module and of the check control module are combined in one control unit.
  
• MID: Multi-information display
  
• MFL: Multifunction steering wheel
  
• PDC: Park distance control
  
• RAD: Radio
  
• AIC: Automatic interval control
  
• TEL: In-car cellular telephone (with eject box)
  
• EWS: Electronic vehicle immobilization, as of 09/96 on K-bus.
  

Identification features of K-bus control units

In the automatic heating and air conditioning control system (IHKA) all functions are operated by push-buttons. In the heating control system (IHR), temperature, air flow and air distribution are adjusted by means of control wheels.

The automatic headlight vertical aim control (LWR) is installed only in conjunction with xenon headlights. In contrast to the manual headlight vertical aim control system, it features no control for vertical adjustment of the headlights.

Function of the K-bus

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 as well as transmit messages via the K-bus.

The K-bus is designed as a single-wire bus system, i.e. the K-bus is a wire system 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 without delay.

Diagnosis with K-bus control units

DIS diagnosis telegrams are sent to the basic instrument cluster via the diagnosis bus (D-bus). From the basic instrument cluster (KOM) the diagnosis telegrams are routed to K-bus control units. The response telegrams of the K-bus control units are sent back also via the basic instrument cluster (KOM) to the DIS.