Limiting Possible Fault Causes

Comfort Data Bus System, Checking

• If the connector is disconnected from a control module connected to the comfort data bus system and the ignition is switched on, a fault entry can occur in the other control modules connected to the comfort data bus system. The same is true if the voltage supply is interrupted by activation of a fuse for example.

• The instrument cluster control module (J285) forms the interface between the two data bus systems. It is also the determining control module in the comfort data bus system. Via adaptation the control modules connected to the comfort data bus system in this vehicle are entered (equipment-dependent). Refer to => Vehicle Diagnosis, Testing and Information System VAS 5051 in the "guided fault finding" function.

• The wiring diagrams can be used to determine how many control modules are connected to the comfort data bus system.

Limiting Possible Fault Causes

• The following fault locations and fault types are provided for the comfort data bus system:

• "Data bus for comfort system"

• Defect: Data cannot be submitted via the data bus system

• In the single-wire mode: No data can be transmitted on one of the two data bus lines ("CAN-Hi "or "CAN-Low")

• Missing messages (time out for several control modules): No data was received from one or more control modules within the defined time period (from the instrument cluster control module (J285), vehicle electrical system control module (J519), steering column electronic systems control module (J527), or comfort system central control module (J393)).

• No communication: No data is received from the instrument cluster control module (J285), comfort system central control module (J393), vehicle electrical system control module (J519) and/or steering column electronic systems control module (J527)

• Read out the DTC memory: The instrument cluster control module (J285), comfort system central control module (J393), vehicle electrical system control module (J519) or steering column electronic systems control module (J527) cannot transmit information due to a fault in an upstream component.

• No communication: No data is received from the auxiliary heater control module (J364) and/or convertible top control module (J256) (prior to further fault finding, check the coding of the instrument cluster control module (J285) and the Climatronic control module (J255) A/C control head and the installation of this optional equipment)

• Read out the DTC memory: The auxiliary heater control module (J364) or convertible top control module (J256) cannot transmit information due to a fault in an upstream component.

• "Powertrain data bus"

• Read out the DTC memory: The instrument cluster control module (J285) cannot transmit information due to a fault in a control module that transmits its data on the powertrain data bus system (query the DTC memory of the instrument cluster control module ( J285). Refer to => Vehicle Diagnosis, Testing and Information System VAS 5051 in the "guided fault finding" function.