Communication Fault

Safety System : Self-Test Fault

The BYTEFLIGHT bus system has a star-shaped structure. The individual satellites (= control modules with/without sensors) are interconnected across a star connector by means of fiber-optic cables. The star connector in the BYTEFLIGHT bus system is the Safety and Gateway Module. There is a transmission and a reception module (transmitter and receiver) as a unit in each satellite for connecting to the BYTEFLIGHT bus. The unit has an integrated transmit and receive diode.

Main functions

Fault memory entries
The procedure for the following fault memory entries is shown below:
1. Self test: too few messages
2. Self test: data fault in message
3. Self test: communication fault
According to a fixed and known pattern, messages are sent during a communication test (self test). A control module transmits a message with known content and this is received and tested by several control modules. During this test, faults 1 to 3 can occur in the receiving control modules.

Two cases are distinguished:

- The receiving control module causes the fault (you can see this from the fact that only one control module has stored the fault)
- The transmitting control module causes the fault (you can see this from the fact that several control modules have stored the fault)

Example: In the control module SBSL (left B-pillar satellite), the "Self-test: data fault in message" fault is stored. Use the following procedure:

- Following the short test, the fault-pattern selection contains the faults of all BYTEFLIGHT control modules. Note down which control modules have stored the "Self test: data fault in message" fault.
- Assuming that the fault memory list indicates that only the control module SBSL has entered the "Self test: data fault in message" fault, then the control module SBSL (left B-pillar satellite) is the cause of the fault.
- Assuming the fault memory list indicates that the control modules SBSL (left B-pillar satellite) and SBSR (right B-pillar satellite) have the "Self-test: data fault in message" fault. As this fault has been stored in the fault memory by several control modules, the fault is being caused by the transmitting control module. The following procedure is required to identify the transmitting control module:
- Cross off the faults found in the fault memory list in Table 2 below.
- The self-created line from Table 2 is compared line by line with Table 1. If a line from Table 1 exactly matches the self-created line from Table 2, you have established that the transmitting control module is the cause of the fault. If you compare Table 1 with Table 2 (with the above example), you identify the transmitting control module: (SGM) Safety and Gateway Module

NOTE: If Table 1 does not help identify the cause of the fault, the cause could also be the Safety and Gateway Module or Safety and Gateway Module connector).

The following Table 1 shows which control modules generate a fault memory entry if a transmitting control module does not send a certain message. The first vertical column contains the transmitting control modules (TCU); the first horizontal line contains the receiving control modules (RCU).

Table 1:







Table 2:







SBSL Satellite, B-pillar left
SBSR Satellite, B-pillar right
SFZ Satellite, vehicle center
SGM Safety and Gateway Module
TMFA Door module, driver
TMBF Door module, passenger
SZL Steering column switch cluster

Service functions

Notes on safety
All work on the airbags must be carried out with the battery disconnected!

Connect and disconnect all BYTEFLIGHT control modules, sensors and generators only with the battery disconnected!

If a fiber-optic cable on the BYTEFLIGHT bus has to be repaired, it must be borne in mind that there may only be one join in a fiber-optic cable. If there is already a join due to a door connector, the fiber-optic cable must not be repaired. In the case of a defect, the fiber-optic cable must be replaced!