System overview, brief description, cars with Trionic T7 engine management system
P-bus and I-bus in the Saab 9-3
All the control modules in the Saab 9-3 are connected to a bus, except for the ABS and SRS. In cars that have traction control, the TCS/ABS control module is connected to the bus.
The bus allows large quantities of information to be exchanged between control modules on only two wires. The bus is divided into a Powertrain bus (P-bus) and Instrument bus (I-bus).
The engine systems Trionic, TCM and TC/ABS require rapid communication so that there are no noticeable delays, for example when limiting engine torque during gearchanges.
The Trionic, TCM and TC/ABS are connected to the P-bus. The data transfer rate on the P-bus is ten times higher than the I-bus.
The P-bus and I-bus are connected to the MIU. The MIU is responsible for ensuring that information available on one bus is also available on the other bus.
The diagnostic tool is not connected directly to the bus but communicates via the DICE, one of the control modules on the I-bus, and thus has access to all control modules connected to the bus.
Vehicle speed is an important item of information for many control modules. Since the ABS is not connected to a I-bus, the vehicle speed signal goes from the ABS to the MIU via a cable of its own. The MIU then sends out the vehicle speed information on the buses. In cars with Traction Control, the MIU receives vehicle speed information from the TC/ABS control module via the P-bus.
The two powertrain systems EDC 15 and the diesel pump are not connected to the I-bus. These systems require much faster communication so that there are no noticeable delays when EDC requests a new fuel mass per injection or a new injection timing, for example.
They are therefore connected by a separate bus called the P-bus (Powertrain Bus). Communication on the P-bus is ten times faster than on the I-bus.
The P-bus is also connected to the MIU. The MIU is responsible for ensuring that information available on one bus is also available on the other bus. Note also that the EDC 15 has a separate K lead for the diagnostic tool.