Bus Communication

P bus and I bus

Two bus information systems, the Powertrain bus (P bus) and the Instrument bus (I bus), are connected to each other in the main instrument unit (MIU). The two buses are electrically separate. The data transfer rate of the P bus is 10 times faster than that of the I bus.
All the information sent out from a control module is available to all other bus-connected control modules. The MIU sees to it that information which is available on one bus is also available on the other bus.
The control modules send out information on the buses are regular times. The interval between two transmissions depends on the type of information transmitted and varies between 10 milliseconds (0.010 seconds)and one second. The information is also transmitted by the control modules each time a change occurs in it.
The transfer of information between the control modules is carried out on two leads, BUS+ (green lead) and BUS- (white lead). Both P bus leads are twisted to reduce their sensitivity to electrical interference.





Diagnostics
In a bus communication system, it is necessary for all units to be capable of communicating with each other. For example, the engine cannot be started unless the Trionic system can receive the immobilization information transmitted by TWICE.

Permanent bus faults
All Tech2 communication with bus-connected systems takes place via DICE. Regardless of which system is contacted, the Tech2 instrument will first check with the aid of DICE that all the car's bus-connected systems are active and in communication. If any bus connected control module is not present, this will be shown on the Tech2. This means that all bus-connected control modules are in proper communication unless the Tech2 indicates otherwise.

Intermittent bus faults
The Trionic system and TCM continuously check that all control modules from which they obtain information communicate correctly. In the event of an intermittent bus communication fault, diagnostic trouble codes will be generated in the Trionic system and TCM. The cause of the fault could be that the control module in question has lost its power supply or one of the bus leads.

Incorrect values on the bus
A diagnostic trouble code will be generated in the Trionic system and TCM if any information they receive on the bus has an incorrect value. In the diagnostic trouble code text, reference is made to the system in which the fault is present.

Bus communication

For further information on the bus refer to Powertrain Management.





The TCM uses the following information:

6C$:

The TCM sends the following Information: