Diagnosis Bus

Diagnosis bus

Introduction

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.

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 TxD 1 cable.
- Access to diagnosis functions requires "Authorization".
- Diagnosis protocol "KWP 2000"(Keyword Protocol 2000).
- Standardized diagnosis structure for all control units.

Diagnosis Concept

The "BMW Fast"(BMW fast access for service and testing) diagnosis concept introduced on the E65/E66 is applied. This concept is based on the "Keyword Protocol 2000"(KWP 2000) diagnosis protocol defined as part of the IS0 14230 standard. Diagnosis communication takes place entirely on the basis of a transport protocol on the CAN bus.

The Diagnosis bus is connected to the Central Gateway Module. All bus systems apart from the MOST bus are connected to the Central Gateway Module (ZGM).

Vehicle Diagnosis Access Point

The diagnosis tool is connected to the vehicle by means of the diagnosis connector OBD ( On-Board Diagnosis ). The connector is located behind a small cover in the drivers side kick panel trim. There is a black plastic cap that bridges KL-30 to the D-bus when the connector is not being used. This cap must be removed before installing the diagnosis cable.







The TxD lead is located in pin 7 of the OBD socket and is connected directly to the ZGM.

The ZGM detects by means of the data transmission speed whether a BMW diagnosis tool (DISplus, MoDiC, GT-1) or an aftermarket scanner is connected.

The DME allows access to different data depending on the diagnosis tool connected.


Note: When using an OBD scan tool for diagnosis, the transmission speed is 10.4 KBit/s.