Failure Of The D-Bus Cable
The following faults can occur to the D-bus wiring:
- D-bus interrupted
- D-bus shorted to battery voltage
- D-bus shorted to ground
- Defective plug connections (damaged, corroded, or improperly crimped)
The operating voltage of the D-bus is 12 volts. The voltage measurement is taken from each data line connection to ground. Each module on the D-bus provides its own voltage.
The fact that 12V are present does not mean that the D-bus is fault free, it just means that the voltage level is sufficient to support communication.
Minimum voltages that are needed for fault free communication are:
- D-bus (TXD)/TXD II > 2.0V
- RXD (if equipped) > 10.5V
If problems are encountered trying to establish communication consider first:
- Battery charge level of the vehicle. Maintain a battery charger on the vehicle at all times during diagnosis.
- Always check that the diagnosis head and connection are OK before working through a test module for lack of communication.
On vehicles that use the IKE/KOMBI as a gateway:
If identification of the vehicle is carried out by the diagnostics without any problems then the D-bus is OK.
If several control units are not recognized this indicates that a bus link is defective. Continue troubleshooting using the test modules for those particular bus systems.