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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, 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:

Information Sensor system
Electrically heated rear window

confirmation (ON/OFF)

DICE

DICE sends electrically heated rear window ON/OFF. When 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).

Vehicle speed

MIU

MIU sends vehicle speed (km/h). The value is used to activate recirculation at high outside temperatures as well as to filter the outside temperature value from SID.

Engine speed

Engine management system

The engine management system sends engine speed (rpm). At an engine speeds below 600 rpm and engine running 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 to calculate the fan current and air distribution position for cold starting.

Unit (Celsius, Fahrenheit)

SID

SID sends temperature unit (Celsius, Fahrenheit). The value is used to show the 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 backlighting.

Rheostat value, Night Panel (0-100%)

SID

SID sends rheostat value for Night Panel 0-100%. The value is used to adjust the button backlighting 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 backlighting.

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

• Indoor Temperature

• Time since start

• Mixed-air temperature

• Fan speed

• Sun radiation.


Outside temperature (˚C)

SID

SID sends outside temperature (˚C). The value is used to calculate the current temperature at head level for front-seat passenger and driver.

The value is damped 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.

Engine running (ON/OFF)

Engine management system

The engine management system sends engine running (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

ACC sends A/C (ON/OFF). ON is sent when ECON is not selected and the outside temperature exceeds 1˚C while fan speed is at least at one bar. The value is used by DICE. Note that there are more blocking conditions in DICE.

Note:

Since the outside temperature value is not allowed to rise unless the vehicle speed exceeds 10 km/h, A/C will not be requested if the outside temperature was below 1 ° C prior to the car being driven into the garage (see activation: 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 to be activated. The value is used by DICE.

Diagnostics communication

DICE/Diagnostics tool

The ACC responds to the diagnostics request from the diagnostics tool via DICE (no unit).