Electrical - 'System Analysis - Signal Fault' Diag. Info
SI B 61 12 09General Electrical Systems
June 2009
Technical Service
SUBJECT
"System Analysis: signal fault" Diagnostics - Important Information
MODEL
F01, F02 (7 Series)
SITUATION
During diagnosis using ISTA, the test plan for "System Analysis: signal fault" is called up, which may lead to a confusing and time-consuming diagnosis.
INFORMATION
General information
The "System Analysis: signal fault" test plan results from "Signal invalid interface faults". These faults belong to the category of so-called event-driven fault code memory entries. Event fault code memory
entries are only used for informational purposes and do not indicate a fault in a control module where the fault is stored. The cause of the event fault is outside the control module (e.g., undervoltage).
Networked systems
In networked systems, the sensor values are made available by control modules connected, for example, by way of bus messages (sent via the bus system) from other bus control modules. If the control module to which the sensor is connected detects an incorrect sensor value, the value is set as invalid in the transmitted bus message ("Signal invalid") and the appropriate fault is stored (e.g., "Coolant temperature, plausibility"). The recipient of this message then sets the appropriate event fault memory
"Invalid signal interface faults". However, this only occurs if the signal failure causes a customer perceptible limitation in the range of the functions of the recipient control module.
Example
After the vehicle test, the following fault memory entries are in the fault list:
DME control module
109408: Coolant temperature sensor, plausibility signal stuck in upper measuring range
IHKA (heating/air conditioning control module), FKA (rear air conditioning control module), and VDM (vertical dynamic management control module)
E7141A: DME interface (engine temperature) signal invalid
E75413: DME interface (engine temperature) signal invalid
D76C80: DME interface (engine temperature signal invalid
Of these, only the fault entry for the coolant temperature sensor (109408) is a component fault.
The three other entries are event fault code memory entries from the various control modules. These systems will now use a default value for the functions, in which the engine temperature is required, meaning that only a reduced level of functionality is available.
In this example, the customer may complain that the heating is not working properly. Therefore, the event fault code memory entry does not mean that the control module in question has a fault, but rather that the cause can be found in the invalid signal received over the bus. All the "Signal invalid interface faults"are combined into one test plan (AT6131_01Signal "System analysis: signal fault").
In the example given above, the "Coolant temperature" test plan should be used for fault elimination. It is only necessary to work through the "System analysis signal fault" test plan when no component faults are stored.
Fault code description
The main benefit of issuing event fault code memory entries is that it makes it possible to trace the effects of the failure of a component in a vehicle. The following information is contained within the fault
code description:
Example: event fault code memory entry for the IHKA E7141A
In the case of a fault with the signal, the defect value for the engine temperature in the IHKA control module is set to 100 C. This can cause unusual heating of the vehicle interior.
Appearance of the fault list
Due to the high levels of interdependence between systems on the F01/F02, there will usually be a relatively long list of fault code memory entries. To make it possible to distinguish the event faults from the component faults, the naming of the former has already been unified to "Interface invalid signal".
This makes it possible to better distinguish them from the component faults at a glance.
Future plans
The numerous event fault messages, a majority of which can be attributed to interface errors, make it more difficult to interpret the fault list.
In the future, event code memory entries will be given their own designation in ISTA. Using a filter, it will then be possible to hide event fault code memory entries.
WARRANTY INFORMATION
Information only
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