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Home >> BMW >> 2004 >> Z4 (E85) L6-3.0L (M54) >> Repair and Diagnosis >> Powertrain Management >> Computers and Control Systems >> Information Bus >> Description and Operation >> Bus Functions - Body >> BYTEFLIGHT Functions (Z Series_Z4-E85/E86) >> Communication Fault >> No Message From Control Module

No Message From Control Module




Safety System: Time-Out Error

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 Information 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 entry: Message (identifier) from control module x missing
According to a fixed and known pattern, a certain message (e.g. A) is transmitted in cycles from a transmitting control module. The receiving control modules 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 memory entry is made in a receiving control module.

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

IMPORTANT: The following tables specify the door satellites STVL and STVR. However, these two door satellites are only fitted in the USA version!







SIM Safety and information module
SBSL Satellite, B-pillar left
SBSR Satellite, B-pillar right
STVL Door satellite, front left
STVR Door satellite, front right

If a "Message (identifier) from control module x missing" fault is entered in a receiving control module, then a message from a transmitting control module 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 modules. 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 modules and the "Message (identifier) from control module x missing" fault is stored in only one receiving control module. There are then the following possible faults:
- Receiving control module or
- Safety and Information Module (SIM) or
- Fiber-optic cable between receiving control module and SIM or
- Plug-in connections to the two control modules (connector not properly engaged, loose contact, etc.)

- Assumption: a message is received by several control modules and the "Message (identifier) from control module x missing" fault is stored in all receiving control modules. There are then the following possible faults:
- Transmitting control module or
- Safety and Information Module (SIM) or
- Fiber-optic cable between transmitting control module and SIM or
- Plug-in connections to the two control modules (connector not properly engaged, loose contact, etc.)

- Assumption: a message is received by several control modules and the "Message (identifier) from control module x missing" fault is stored in a number of receiving control modules (not all!). Then a general statement is no longer possible. The defect might then lie at the connector of the Safety and Information Module.

In order to precisely identify whether the control module or fiber-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 memory entry: "Message (identifier) from control module x missing"
Assuming that the "Message (7) from SBSR missing" fault is stored in one control module (e.g. SBSL). Use the following procedure:
- Look for the row in the Table that contains the transmitting control module (TCU) SBSR with message (7).
- From the Table, establish which control modules are receiving this message. For the above example, these are the control modules SBSL, SIM, STVL and STVR.
- Display the fault memory list of the control modules SBSL, SIM, STVL and STVR from the short test and fault-pattern selection (other option: switch to "Control-Module Functions" of these control modules and read the fault memory)
- If the "Message (7) from SBSR missing" fault is entered in all receiving control modules SBSL, SIM, STVL and STVR, then there are the following possible faults:
- Transmitting control module SBSR
- Safety and Information Module (SIM)
- Fiber-optic cable between SBSR and SIM
- Plug-in connections at the two control modules

- If the "Message (7) from SBSR missing" fault is only entered in one receiving control module, e.g. SBSL, then there are the following possible faults:
- Receiving control module SBSL
- Safety and Information Module (SIM)
- Fiber-optic cable between SBSL and SIM
- Plug-in connections at the two control modules

- In order to precisely identify whether the control module or fiber-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 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 between the Safety and Information Module and a satellite. For this reason, no repairs may be performed on the fiber-optic cable between the Safety and Information Module and the door satellites, as there is already a join with the door connector. In the case of a defect, the fiber-optic cable must be replaced!
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