Bus communication

Bus communication

•	Trionic T7 control module (430)

•	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 (TC/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.

Information transfer between control modules takes place via two leads, BUS+ (green led) and BUS- (white lead). On the P bus, the two leads are twisted to reduce sensitivity 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.

Missing control module	DTC
TCM	P1923
MIU	P1908
TWICE	P1902
DICE	P1901

Intermittent bus faults

The Trionic and TCM control modules continuously check that all control modules from which they receive information are in proper communication. Intermittent bus communication faults will cause diagnostic trouble codes to be generated in the Trionic T7 and TCM control modules. The cause of the fault may be that the supply of current to the control module concerned has failed or that one of the bus leads is broken or disconnected.

Incorrect values on the bus

A diagnostic trouble code will be generated in the Trionic T7 and TCM control modules if any information they obtain from the bus has an incorrect value. The diagnostic trouble code text indicates the system where the fault is located.

The Trionic T7 uses the following information:

Information	Unit	Sensor system	Description
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.
Sport 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 TC/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 A/C request, unit ON/OFF. The value is used in the air mass control, compensation, to compensate for the increase in load. The 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.
Brake lights	ON/OFF	TWICE	TWICE sends brake lights, unit ON/OFF. The value is used for the cruise control function and for diagnosis of the speed signal from the ABS.
Immobilization	ON/OFF	TWICE	TWICE sends immobilizer, unit ON/OFF. The value is used in the fuel injection system to activate fuel shut-off.
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/diagnostics instrument	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	Unit	User System	Description
Engine torque	Nm	TCM	The current mass air flow/combustion is converted into torque, unit Nm. The value is used by the TCM.
Accelerator 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 into a corresponding accelerator pedal position, unit %. The value is used by the 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 has started	rpm	ACC, DICE	ON is sent, unit ON/OFF, 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 consumed 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.