Bus Communication

P-bus and I-bus

All the control modules in the Saab 9-5 are connected to the bus except those for the ABS and SRS.
The bus is divided into a Powertrain bus (P-bus) and an Instrument bus (I-bus).
The data transfer rate 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 other control modules on the bus. The MIU is responsible for ensuring that information available on one bus is also available on the other bus.

The control modules send information to the bus at regular intervals. The time between two transmissions depends on what information is being sent and varies between 10 milliseconds (0.010 seconds) and one second. The control module also sends information every time the information changes.
Information is transmitted between control modules on two leads, BUS+ (green lead) and BUS- (white lead). Both P-bus leads are twisted to reduce their sensitivity to electrical interference.
On MIU connected to both the I-bus and the P-bus, the twisted leads are connected to the following pins of the 12-pin connector:

I-bus: Pin 5 (green lead Bus+) Pin 12 (white lead Bus-)
P-bus: Pin 4 (green lead Bus+) Pin 11 (white lead Bus-)

Diagnosis
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 immobilizer information 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 bus-connected control module is missing, Tech 2 will detect this. This means that all the bus-connected control modules are communicating correctly if there is no warning from Tech 2.

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

Incorrect values on the bus
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.
For further information about the bus, see Diagnostics communication.
See Powertrain Management/Computers and Control Systems/Information Bus

DICE communication, lighting:









SID communication, lighting: