Safety system: timeout error

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 entry: Message (identifier) from control unit x missing

According to a fixed and known pattern, a certain message (e.g. 9) is transmitted in cycles from a transmitting control unit. The receiving control units that expect this message in cycles can determine whether this message is missing or arrives too late. If this fault is detected, the above fault code memory entry is made in a receiving control unit.

The table below shows which messages are sent and/or received by which control unit. The first vertical column contains the transmitting control units (TCU); the first horizontal line contains the receiving control units (RCU). A transmitting control unit can transmit various messages to the receiving control units. A certain message is indicated by the identifier in brackets below the transmitting control unit. This table can be used to determine which receiving control units have to generate a fault code memory entry if a message from the transmitting control unit fails. If, for example, the Safety and Gateway Module is no longer transmitting message 9, the fault code memory entry ”Message (9) from Safety and Gateway Module missing” is created in the SBSL (left B-pillar satellite), SBSR (right B-pillar satellite), TMFA (door module, driver) and TMBF (door module, passenger).

If a ”Message (identifier) from control unit x missing” fault is entered in a receiving control unit, then a message from a transmitting control unit has failed. In order to locate the cause of the fault, it must first be determined whether this fault is also entered in other receiving control units. In this way, the cause of the fault can be located. In this context, three cases are distinguished:

• Assumption: a message is received by several control units and the ”Message (identifier) from control unit x missing” fault is stored in only one receiving control unit. There are then the following possible faults:
  
  • Receiving control unit or
    
  • Safety and Gateway Module (SGM) or
    
  • Fibre-optic cable between receiving control unit and SGM or
    
  • Plug-in connections to the two control units (connector not properly engaged, loose contact, etc.)
    
• Assumption: a message is received by several control units and the ”Message (identifier) from control unit x missing” fault is stored in all receiving control units. There are then the following possible faults:
  
  • Transmitting control unit or
    
  • Safety and Gateway Module (SGM) or
    
  • Fibre-optic cable between transmitting control unit and SGM or
    
  • Plug-in connections to the two control units (connector not properly engaged, loose contact, etc.)
    
• Assumption: a message is received by several control units and the ”Message (identifier) from control unit x missing” fault is stored in a number of receiving control units (not all!). Then a general statement is no longer possible. The defect might then lie at the connector of the Safety and Gateway Module.
  In order to precisely identify whether the control unit or fibre-optic cable is defective, the BYTEFLIGHT bus must be tested optically! The test programs for the optical test on the BYTEFLIGHT bus can be found under function selection: Body, Bus Functions, BYTEFLIGHT Functions and Optical Test.
  

Procedure in the case of fault code memory entry: ”Message (identifier) from control unit x missing”

Assuming that the ”Message (1) from TMFA missing” fault is stored in one control unit (e.g. SBSL). Use the following procedure:

• Look for the row in the Table that contains the transmitting control unit (TCU) TMFA with message (1).
  
• From the Table, establish which control units are receiving this message. For the above example, these are the control units SBSL and TMFA.
  
• Display the fault code memory list of the control units SBSL and TMFA from the quick test and fault-pattern selection (other option: switch to ”Control Unit Functions” of these control units and read the fault code memory)
  

• If the ”Message (1) from TMFA missing” fault is entered in all receiving control units SBSL and TMFA, then there are the following possible faults:
  
  • Transmitting control unit TMFA
    
  • Safety and Gateway Module (SGM)
    
  • Fibre-optic cable between TMFA and SGM
    
  • Plug-in connections at the two control units
    
• If the ”Message (1) from TMFA missing” fault is only entered in one receiving control unit, e.g. SBSL, then there are the following possible faults:
  
  • Receiving control unit SBSL
    
  • Safety and Gateway Module (SGM)
    
  • Fibre-optic cable between SBSL and SGM
    
  • Plug-in connections at the two control units
    
• In order to precisely identify whether the control unit or fibre-optic cable is defective, the BYTEFLIGHT bus must be tested optically. The test programs for the optical test on the BYTEFLIGHT bus can be found under function selection: Body, Bus Functions, BYTEFLIGHT Functions and Optical Test.
  

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!