P-bus and I-bus
All Saab 9-3 M99 are equipped with the Trionic T7 engine management system. The bus system is therefore almost identical to the one fitted on the 9-5.
The bus system on diesel cars with EDC15 and diesel pump is unchanged from M98 1/ and on cars with PSG 16 from M01 1/2.
The two diesel engine systems EDC15/diesel pump and PSG 16 are not connected to the bus however. These systems require considerably faster communication to avoid any noticeable delays, e.g. when EDC or PSG requests a certain amount of fuel for injection.
Therefore, they are connected to a separate bus called the P-bus (Power-train Bus). The data transfer rate on the P-bus is ten times greater than that of the I-bus.
The P-bus is also connected to the MIU (Main Instrument Unit). The MIU is responsible for ensuring that information which is available on one of the buses is also made available on the other bus.