Bus communication

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 M2.10.3 (505)

•	Control module ACS (509)

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MIU (540)

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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 meaning.

Serial means that the information is sent in ”packages” in rapid succession.

In the Saab 9-3, half of all control modules are connected to a bus.

The buses are split up in P-bus (Powertrain Bus) and 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, it 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 have a need for 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:

Information	Sensor system
Electrically heated rear window confirmation (ON/OFF)	DICE	DICE sends electrically heated rear window ON/OFF. For ON, the button symbol is shown on the display.
Ignition +50	DICE	DICE sends +50 activated
Steering wheel position	TWICE	TWICE sends steering wheel position (right/left).
Travelling speed	MIU	MIU sends travelling speed (km/h). The value is used to activate recirculation at high outside temperature, as well as for filtering the outside temperature value from SID.
Engine speed	Engine management system	The engine management system sends engine speed (rpm). At an engine speed below 600 rpm and with the engine has started OFF, the fan current is limited to 5 A.
Coolant temperature	Engine management system	The engine management system sends coolant temperature (˚C). The value is used for calculating fan current and air distribution position for cold starts.
Units (Celsius, Fahrenheit)	SID	SID sends temperature unit (Celsius, Fahrenheit). The value is used to indicate selected temperature unit on the display.
Language (English, German, French, Spanish, Swedish, Italian)	SID	SID sends selected language. The value is used to write text messages on the SID using the selected language.
Rheostat value (0-100%)	SID	SID sends rheostat value (%). The value is used to adjust the button background lighting.
Rheostat value, Night Panel (0-100%)	SID	SID sends rheostat value for Night Panel 0-100%. The value is used to adjust the button background lighting when Night Panel is ON.
Night Panel (ON/OFF)	SID	SID sends Night Panel (ON/OFF). When ON, the display goes off.
Display lighting (0-100%)	SID	SID sends display lighting value (%). The value is used to control the display background lighting.
Time Engine Off (minutes)	SID	SID sends time in minutes that the engine has been turned off. The value is used to calculate present temperature at head level for front-seat passenger and driver. Additional input values include: • Outside temperature • Cabin temperature • Time since start • Mixed-air temperature • Fan speed • sun radiation.
Outside temperature (˚C)	SID	SID sends the outside temperature (˚C). The value is used to calculate actual temperature at head level for front seat passenger and driver. The value is reduced and filtered in the ACC unit and can therefore differ from the value shown on the SID display.
Soft top down	STC	STC sends soft top down ON/OFF.
The engine has started (ON/OFF)	Engine management system	The engine management system sends the engine has started (ON/OFF). When OFF and engine speed is under 600 rpm, fan current is limited to 5 A.

The ACC sends out the following information:

Information	User system
Text message	SID	The ACC sends Text message when additional user programming is programmed/cancelled. The value is used by SID.
Sound	SID	The ACC sends Sound when additional user programming is programmed/cancelled. The value is used by SID.
A/C	DICE	The ACC sends A/C (ON/OFF). ON is sent when ECON is not selected and the outside temperature exceeds 1˚C with the fan speed at the lowest setting. The value is used by DICE. Note that other blocking conditions are present in DICE. Note: As the outside temperature value is not allowed to rise unless vehicle speed is over 10 km/h, A/C will not be requested if outside temperature was under 1˚C before the car was driven into the workshop (see activating: Outside temperature 20˚C).
Electrically heated rear window	DICE	The ACC sends Electrically heated rear window (ON/OFF). ON is sent when Electrically heated rear window is activated. The value is used by DICE.
Diagnostics communication	DICE/Diagnostics tool	The ACC replies to the diagnostics request from the diagnostics tool via DICE (unit missing).