Bus Communication

Bus Communication








P bus and I bus
All the control modules in the Saab 9-5 are connected to the bus with the exception of ABS and SRS.

The bus is divided into a Power train bus (P bus) and an Instrument bus (I bus). Both busses are connected to the main instrument display panel (MIU). The busses have separate electrical systems.

Data transmission on the P bus is ten times faster than on the I bus.

All the information sent from one control module is accessible for all the other control modules on the bus. The MIU is responsible for making information on one bus available to the other bus.

The control modules sends information to the bus at regular intervals. The time between two transmissions depends on which information is being sent and varies between 10 milliseconds (0.010 seconds) and one second. The control module also sends information every time it changes.

Information is transmitted between control modules on two leads, BUS+ (green lead) and BUS- (white lead). Both P bus leads are twinned to decrease sensitivity to electrical interference.

Diagnostics
In a bus system, all the units must be able to communicate with each other. For example. the engine cannot be started if Trionic is unable to receive information on the immobilizer from TWICE.

Permanent bus faults
All communication between Tech 2 and the bus-connected systems goes via DICE. Irrespective of which system is being contacted, Tech 2 and DICE will check to see that all the bus-connected systems in the car are activated and communicating. If any of the bus-connected control modules are missing, Tech 2 will detect this. This means that all the bus-connected control modules are communicating correctly if Tech 2 does not give a warning.

Intermittent bus faults
Trionic and TCM check continuously to see that all the control modules they receive information from are communicating correctly. In the event of an intermittent fault occurring in the bus communication, a diagnostic trouble code will be set in Trionic and TCM. The cause of the fault can be that the power supply or one of the bus leads to the control module in question is absent.

Bus value error
Diagnostic trouble codes are set in Trionic and TCM if any information they receive from the bus has an incorrect value. The trouble code readout will refer to the faulty system.





DICE uses the following information





DICE sends the following information