Body System Faults

General Electrical Faults

The electrical system of a modern car if a highly complicated network of linked data buses. In order to reduce the quantity of wiring in a modern car networks were introduced in the 1990′s. They were originally single wire LIN-BUS networks that operated at a slow speed to control the functions of the car. Later technologies introduced CAN-BUS that enabled more controllers to operate on a single network at a much faster rate. We are now seeing optical networks and FLEX-RAY networks that can carry data at incredible rates around the car.

wiseman mascotAll of the functions of a modern car are operated by controllers modules. These are each linked by a network. For example in a door you may have a window motor, a window switch, a door lock, a electric mirror adjuster. These items are all modules on the network and they communicate to each other using binary coding, i.e. a series of voltage pulses that indicate a 1 or a 0 to the other modules on the network. When a module sends a message it will include an address and an instruction to the module with that address. When the instruction is received, the corresponding module carries out the request.

For example, the window switch module is pressed and the module sends a message on the network to the window motor which receives the instruction, carries out the request and sends an acknowledgement back to the switch.

Networks are interlinked via gateways and messages are sent from module to module around the car through these networks. The speed of these networks differ dependant on the nature of the modules using them. Safety critical networks, such as ABS and Airbag, work at a much faster rate than non after such as engine management and body control.

If a controller or module fails it can affect other functions on that network, this is often seen when similar functions fail at the same time. Sometimes the network is corrupted by a static voltage on the data bus that prevents the messages traveling around the network.

Any break or damage to the wiring will cause a failure and this is common in door wiring or in controllers that suffer from water ingress due to their location in the vehicle.

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