P-Bus And I-Bus
WARNING: This page is about a different car, the 2001 Saab 9-3. However, it is still accessible from the selected car via links, so may be relevant.
The two powertrain systems EDC and diesel pump are not connected to the bus. These systems require considerably faster communication to avoid noticeable delays, e.g. torque limitation when changing gear.
Therefore, they are connected to a separate bus called the P-bus (Powertrain Bus). The data transfer rate on the P-bus is ten times faster than on the I-bus.
The P-bus is also connected to the MIU. The MIU ensures that information which is available on one of the buses will also be available on the other bus.