Centralized Fault Memory

This subfunction has the task of centralized storage of fault and Check Control messages in addition to the local fault memories for each of the control units and the storage of CC messages in the instrument panel. The central gateway module (ZGM) is the master for this function and it is also called the Diagnostics Master.

Whenever faults occur, all control units locally save the fault along with at least the two mandatory environmental conditions of kilometer reading and system time. A new function is that the control units additionally signal the fault code and the system time at which the fault occurred (time stamp) to the Diagnostics Master (ZGM).

The fault memory concept and fault memory process of the control units have not been changed by the additional reporting to the Diagnostics Master. This means a control unit "very normally" makes a self-defined fault memory entry. The local fault memory entry remains untouched in the local fault memory of the secondary control unit.

The Diagnostics Master then additionally centrally stores the fault code and a fixed set of 26 ambient conditions at the same time that it indicated in the time stamp.

The ambient conditions stored on the fault message by the Diagnostics Master include different information on the global status of the vehicle such as the:

• Standard time
• Vehicle system voltage
• Outside temperature
• Terminal status
• Kilometer reading
• Vehicle driving speed

The central fault memory in the ZGM has a size of 18 kB. Between 250 and 1000 fault events and Check Control messages can be stored centrally in the ZGM dependent upon how many faults occur simultaneously. When the fault memory is full no new faults or Check Control messages are stored. The fault and Check Control messages in the central fault memory can then only be deleted via the BMW diagnostic system.

Each fault code and each Check Control message is accepted up to 10 times. Without this limit, a constantly occurring fault would very quickly fill the entire central fault memory.

These ten entries are sufficient for analysis of the fault.

All central fault memory entries are lost when the ZGM is replaced.

Advantages:

Previously (without Diagnostics Master), only the kilometer reading and system time (mandatory environmental conditions) and possibly a few additional ambient conditions could be found in the local fault memories.

The ZGM stores 26 additional ambient data items for each fault memory entry from each of the control units.

Additionally, up to 10 time instances at which the fault occurred are recorded in the ZGM for a fault code.

The time stamp with second-precision permits a statement upon the time sequence of fault events, which was previously not possible based solely upon the kilometer reading. For the first time it is possible to the name the cause and effect with greater clarity for distributed functions, e.g. the control unit that firstly entered a fault, the control unit that in consequence only entered a fault as a reaction, etc.

The Check Control messages at the time of the fault are also stored in the Diagnostics Master and are also provided with the 26 ambient conditions. "Customer complaints" can be assigned better to a vehicle situation because of the Check Control messages and above all also corresponding fault memory entries.

These measures have made a more precise diagnosis possible.

Index	Explanation
1	Two local ambient conditions for fault 1
2	Fault 1 and 2 local ambient conditions are stored in the fault memory of the control unit
3	Fault message 1 (FM1) and the "time stamp" are sent to the Diagnostics Master
4	Central ambient conditions at the time when fault 1 occurred
5	Ambient conditions at the time when fault 2 occurred
6	Diagnostics Master in the ZGM
7	Fault message 2 (FM2)
8	Fault message 1 (FM1)
9	Fault message 2 (FM2) and the "time stamp" are sent to the Diagnostics Master
10	Fault 2 and 2 local ambient conditions are stored in the fault memory of the control unit
11	Two local ambient conditions for fault