Diagnosis Bus: Introduction

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The aim of diagnosis is to enable a Technician to reliably identify a defective component. By the use of appropriate hardware and monitoring software, the microprocessor of a control unit, for example, is able to detect faults in the control unit and its peripherals.

Fig 1: Identifying Diagnosis Bus

Courtesy of BMW OF NORTH AMERICA, INC.

Faults identified are stored in the fault memory and can be read out using the Diagnosis Program. Data transfer between the vehicle and the diagnosis tool takes place via the Diagnosis bus (D bus). The new features of the diagnosis bus are:

Faster data transmission speed of 115 kBd.
Central diagnosis access point (OBD connector).
Single diagnostic cable (TxD II) for the entire vehicle.
Omission of the TxD1 cable.
Access to diagnosis functions requires "Authorization".
Diagnosis protocol "KWP 2000" (Keyword Protocol 2000).
Standardized diagnosis structure for all control units.