Bus System Troubleshooting: Introduction

Up until the introduction of the E31, all information (e.g. RPM, temperature, vehicle speed, etc.) received and transmitted from a control unit were delivered by a dedicated wire. As the electronic systems used in the vehicle increased, so did the necessary wiring.

Wiring each device separately became a headache for production and finding space in the body to hold all of this wiring was becoming difficult, not to mention the effect on reliability and ever more complicated troubleshooting.

It soon became clear that a solution must be found, that solution was the bus system. The benefits of the bus system are:

• Greater reliability by reducing the number of wiring, connectors and components.
• Reduction in wire harness size by decreasing the number of interfaces between control units to one or two wires.
• Multiple utilization of sensors by transmitting information from one control unit to the next.
• Flexibility in system configuration and future applications.
• Reduction in costs for components, assembly and troubleshooting.

Today's vehicles have several bus systems that are divided according to groups of control units which share common functionality and information. Currently the bus systems in use are:

• CAN-bus.
• D-bus.
• l-bus.
• K-bus.
• P-bus.
• M-bus.

In the very near future the complexity and number of control units in the vehicle will change, as will the structure and construction of the bus systems. However, the principle of operation will remain similar. Efficient troubleshooting of the new bus systems will rely on a thorough understanding and knowledge of the systems currently in use.