Safety system: self-test fault

The BYTEFLIGHT bus system has a star-shaped structure. The individual satellites (= control units with/without sensors) are interconnected across a star coupler by means of fibre-optic cables. The star coupler 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 code memory entries

The procedure for the following fault code 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 unit transmits a message with known content and this is received and tested by several control units. During this test, faults 1 to 3 can occur in the receiving control units.
   

Two cases are distinguished:

• The receiving control unit causes the fault (you can see this from the fact that only one control unit has stored the fault)
  
• The transmitting control unit causes the fault (you can see this from the fact that several control units have stored the fault)
  Example: In the control unit SBSL (left B-pillar satellite), the ”Self-test: data fault in message” fault is stored. Use the following procedure:
  
  • Following the quick test, the fault-pattern selection contains the faults of all BYTEFLIGHT control units. Note down which control units have stored the ”Self test: data fault in message” fault.
    
  • Assuming that the fault code memory list indicates that only the control unit SBSL has entered the ”Self test: data fault in message” fault, then the control unit SBSL (left B-pillar satellite) is the cause of the fault.
    
  • Assuming the fault code memory list indicates that the control units 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 code memory by several control units, the fault is being caused by the transmitting control unit. The following procedure is required to identify the transmitting control unit:
    
    • Cross off the faults found in the fault code 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 unit is the cause of the fault. If you compare Table 1 with Table 2 (with the above example), you identify the transmitting control unit: (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 units generate a fault code memory entry if a transmitting control unit does not send a certain message. The first vertical column contains the transmitting control units (TCU); the first horizontal line contains the receiving control units (RCU).

Table 1:

Table 2:

Service functions

Notes on safety

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

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

If a fibre-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 fibre-optic cable. If there is already a join due to a door connector, the fibre-optic cable must not be repaired. In the case of a defect, the fibre-optic cable must be replaced!