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Bus communication

Bus communication



Trionic T7 control module (600)

TCM control module (502)

MIU control module (540)

DICE control module (628)

Data link connector (445)

SID control module (541)

Audio control module (353)

ACC control module (216)

CD changer control module (355)

PSM control module (357)

TWICE control module (632)

PMM control module (611)

ABS (547), TC/ABS (382) control modules

Airbag control module (331)


P bus and I bus


In the Saab 9-5, all the car's control modules are connected to buses with the exception of the ABS and SRS control modules.

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

The P bus has a data transfer rate 10 times higher than that of the I bus.

All information sent out by a control module is available to all other control modules connected to the bus. The MIU ensures that the information which is available on one bus is also available on the other.

The control module sends out information on the bus at regular intervals. The time between two transmissions depends on which information is being transmitted and varies between 10 milliseconds (0.010 seconds) and one second. Information is also sent out by the control module whenever the information changes.

The transfer of information between the control modules takes place on two leads, BUS+ (green lead) and BUS- (white lead). The two leads are twisted to make them less sensitive to electrical interference

Diagnostics

In a bus system, all units must be able to communicate with each other. For example, the engine cannot be started unless the Trionic T7 can receive the immobilization information sent out by TWICE.

Permanent bus faults

All communication between the diagnostic tool and systems connected to the bus takes place through DICE. Irrespective of which system is contacted, the diagnostic tool first checks by means of DICE that all on-board systems connected to the bus are turned on and in communication. If any control module connected to the bus is missing, the diagnostic tool will show this. This means that all control modules connected to the bus can communicate properly unless the diagnostic tool warns otherwise.

Intermittent bus faults

Trionic continuously checks that TCM and MIU are communicating correctly. Diagnostic trouble codes will be generated if intermittent fault should occur. The cause of such faults may be that the control module has lost its power supply or one of the bus leads.

Missing control module DTC
TCM

P1923

MIU

P1908



The Trionic T7 uses the following information:

Information Sensor system
Maximum permitted torque (Nm)

TCM

The TCM sends maximum permitted torque, unit Nm. The value is used in the mass air flow control system for torque limitation.

Sports mode selected (ON/OFF)

TCM

The TCM sends sports mode, unit ON/OFF. The value is used in the mass air flow control system to correct the pedal position conversion to the requested mass air flow/combustion.

Selector lever position, automatic gearbox (PRND321)

TCM

The TCM sends selector lever position, unit PRND321. The value is used in the mass air flow control system for idle speed control.

Vehicle speed, left rear wheel (km/h)

MIU

The MIU sends speed, unit km/h. The value is used by the cruise control and as a substitute if the speed signal from ABS disappears.

Reverse gear selected (ON/OFF)

DICE

DICE sends reverse gear selected, unit ON/OFF. The value is used to determine whether first gear or reverse is engaged as the gear ratio does not adequately distinguish between these gears.

A/C request (ON/OFF)

DICE

DICE sends out A/C request, unit ON/OFF. The value is used in the mass air flow control system, compensation, to compensate for the load increase. The Trionic control module also activates the A/C relay.

A/C pressure, high pressure side (bar)

DICE

DICE sends pressure, unit bar. The value is used in the mass air flow control system, compensation, to calculate the load increase before the A/C compressor is activated.

Current consumption (A)

DICE

DICE sends calculated current consumption of the electrically heated rear window and radiator fan immediately before they are activated, unit A. The value is used in the mass air flow control system, compensation, to compensate for the load increase.

Fast idling speed (ON/OFF)

DICE

DICE sends fast idling speed, unit ON/OFF. ON is sent if the radiator fan is activated for high-speed during the present driving cycle. The value is used in the idling speed control.

Immobilizer (ON/OFF)

TWICE

TWICE sends immobilizer, unit ON/OFF. The value is used in the fuel injection system to activate fuel shut-off.

Brake lights (ON/OFF)

TWICE

TWICE sends out brake lights, unit ON/OFF. The value is used to limit engine torque when the brake pedal is depressed.

Ignition +50 circuit (ON/OFF)

DICE

DICE sends out +50, unit ON/OFF. The value is used for diagnosis of the crankshaft position sensor.

Diagnostics

DICE/diagnostic tool

The diagnostic tool sends diagnostic request via DICE, unit missing. The value is used to respond to the request concerned.



The Trionic T7 sends out the following information:

Information User System
Engine torque (Nm)

TCM

The current mass air flow/combustion is converted into torque, unit Nm. The value is used by the TCM.

Accelerator pedal position (%)

TCM

The highest requested value for mass air flow/combustion from the accelerator pedal position or cruise control is selected. The value is converted to a corresponding accelerator position, unit %. The value is used by TCM.

Kickdown (ON/OFF)

TCM

When the voltage from pedal potentiometer 1 corresponds to the kickdown position (less than 1.50 V), kickdown ON, unit ON/OFF, is sent. The value is used by the TCM.

Engine speed (rpm)

MIU, TCM and ACC

The current engine speed is sent, unit rpm. The value is used by the TCM, ACC and MIU.

Coolant temperature (°C)

MIU, DICE and ACC

The current temperature is sent, unit °C. The value is used by ACC, MIU and DICE.

Engine running (ON/OFF)

ACC, DICE

ON, UNIT ON/OFF, is sent when engine speed exceeds 650 rpm. The value is used by the ACC and DICE.

CHECK ENGINE (ON/OFF)

MIU

ON, unit ON/OFF, is sent when On-board diagnostics reports that the lamp should be lit. The value is used by the MIU.

SHIFT UP (ON/OFF)

MIU

ON, unit ON/OFF, is sent when running with a light load and high rpm, and at very high rpm irrespective of load. The value is used by the MIU.

CRUISE lamp (ON/OFF)

MIU

ON, unit ON/OFF, is sent when cruise control is activated with the switch. The value is used by the MIU.

Fuel used since start (ml)

MIU, SID

The value is 0 ml when the ignition is switched on and is then incremented for each injection, unit ml. The value is used by the MIU.

Diagnostics

DICE/diagnostic tool

The Trionic T7 answers the diagnosis request from the diagnostic tool via DICE, unit missing.