Bus Communication, ACC

Bus Communication

- Control module, ACC (216)
- Radio connector C (267c)
- Control module airbag/SRS (331)
- Radio (353)
- CD-changer (355)
- Control module, PSM (357Dk)
- Control module, Trionic (430)
- Control module, TCM (502)
- Control module, ACS (509)
- MIU (540)
- SID (541)
- Control module (ABS) 547
- Control module, Soft Top opening STC (565)
- Control module M4.1 (586)
- Control module, Trionic OBDII (589)
- Control module, diesel system (595)
- Control module, auxiliary heater (597)
- Diesel pump (598)
- Control module, DICE (628)
- Control module, TWICE (632)


P-bus and I-bus







The term bus refers to leads where the information is sent digitally or serially. Digital means that the voltage differential between two leads only can have two values, approximately 0 and 5 V. The information is coded so that different combinations of pulses with values 0 and 5 V have different meanings.


Serial means that the information is sent in "packets" in rapid succession. In the Saab 9-3, half of all control modules are connected to a bus.


The bus is divided into a P-bus (Powertrain Bus) and an I-bus (Instrument bus). Both buses are connected to the main instrument unit (MIU). The buses are electrically isolated from each other.


The diagnostics tool is not directly connected to a bus but communicates with DICE, one of the control modules connected to the I-bus, and therefore has access to all other control modules connected to a bus.


The P-bus has a communication speed that is ten times that of the I-bus. The reason for this is that the powertrain Systems require information with minimal delay.


All information sent out by control modules is available to all other control modules connected to a bus. MIU is responsible for making sure that information available on one bus also is available on the other bus.


The control modules send out information on 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 1 second. The information is also sent out by the control modules each time that the information is changed.


The transfer of information between the control modules occurs on two leads, bus+ (green lead) and bus- (white lead). The leads are twisted in order to increase tolerance to electric interference.

The ACC uses the following information:

Part 1:

Part 2:

The ACC sends the the following information: