Bus communication

Bus communication

•	Control module, ACC (216)

•	Radio connector C (267c)

•	Airbag/SRS control module (331)

•	Radio (353)

•	CD changer (355)

•	PSM control module (357Dk)

•	Control module, Trionic T7 (430b)

•	MIU (540d)

•

SID (541)

•	ABS control module (547)

•	STC control module (565)

•	Control module, Trionic T7 OBDII (589b)

•	Control module, DICE (628)

•	Control module, TWICE (632)

P-bus and I-bus

All the control modules in the Saab 9-5 are connected to the bus with the exception of ABS and SRS.

The bus is 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.

Data transfer is 10 times faster on the P-bus than on the I-bus.

All the information transmitted by one of the control modules is available to all the other control modules connected to the bus. MIU is responsible for making the information that is available on one bus also available on the other bus.

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

Information between the control modules is transferred through two leads, BUS+ (green lead) and BUS- (white lead). The two leads are twisted on the P-bus to reduce sensitivity to electrical interference.

Diagnostics

In a bus system, it is necessary for all the units to be able to communicate with each other. For example, the engine cannot be started unless Trionic T7 can receive immobilizer information transmitted by TWICE.

Permanent bus faults

All communications between the diagnostic tool and systems on the bus take place via DICE. Irrespective of which system is being contacted, the diagnostic tool, with the help of DICE, will make sure that all the systems on the bus are active and communicating. The diagnostic tool will indicate any control modules missing from the bus. This means that all the control modules are communicating correctly on the bus unless the diagnostic tool warns otherwise.

Missing control module	Diagnostic trouble code
TCM	P1923
MIU	P1908
TWICE	P1902
DICE	P1901

Intermittent bus faults

Trionic and TCM check continuously that all the control modules they retrieve information from are communicating correctly. Diagnostic trouble codes will be generated in Trionic T7 and TCM if a fault should occur in bus communications. The cause of the fault may be that the control module in question has lost its power supply or one of the bus leads is missing.

Incorrect bus values

Diagnostic trouble codes will be generated in Trionic T7 and TCM if the value of any information they retrieve on the bus is incorrect. The diagnostic trouble code message refers to the system in which the fault can be found.

Trionic T7 uses the following information:

Information	Unit	Sensor system	Description
Maximum permissible torque	Nm	TCM	TCM sends maximum permissible torque, unit Nm. The value is used in the air mass control for engine torque limitation.
Sport position selected	ON/OFF	TCM	TCM sends sport position, unit ON/OFF. The value is used in the air mass control to correct the conversion of the pedal position to requested air mass/combustion.
Selector lever position, automatic transmission	PRND321	TCM	TCM sends selector lever position, unit PRND321. The value is used in the air mass control for idle speed control.
Vehicle speed, rear left wheel	km/h	MIU	MIU sends speed, unit km/h. The value is used by cruise control and as a substitute value if the speed signal from ABS disappears.
Reverse gear selected	ON/OFF	DICE	DICE sends reverse gear engaged, unit ON/OFF. The value is used to determine if first gear or reverse gear is engaged as the gear ratio is not enough to distinguish between them.
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 air mass control, compensation, to calculate the increase in load before the A/C compressor is activated.
Current consumption	A	DICE	DICE sends the calculated current consumption of the electrically heated rear window and radiator fans just before they are activated, unit A. The value is used in the air mass control, compensation, to compensate for the increase in load.
Brake lights	ON/OFF	TWICE	TWICE sends brake light, unit ON/OFF. The value is used for the cruise control function and diagnosis of the speed signal from ABS.
Immobilizer	ON/OFF	TWICE	TWICE sends immobilizer, unit ON/OFF. The value is used in the fuel injection to activate fuel shut-off.
Ignition +50	ON/OFF	DICE	DICE sends +50, unit ON/OFF. The value is used for diagnosis of the crankshaft position sensor.
Diagnostics		DICE/diagnostic tool	The diagnostic tool sends a diagnostics request via DICE, no unit. The value is used to respond to the current request.

Trionic T7 transmits the following information:

Information	Unit	User system	Description
Engine torque	Nm	TCM	Current air mass/combustion converted to engine torque, unit Nm. The value is used by TCM.
Accelerator pedal position	%	TCM	The highest of the air mass/combustion values requested from the accelerator pedal position or cruise control is selected. The value is converted to a corresponding accelerator pedal position, unit %. The value is used by TCM.
Kickdown	ON/OFF	TCM	When the voltage from pedal potentiometer 1 corresponds with the kickdown position (below 1.50 V), kickdown ON, unit ON/OFF is sent. The value is used by TCM.
Engine speed	rpm	MIU, TCM and ACC	Current engine speed is sent, unit rpm. The value is used by TCM, ACC and MIU.
Engine coolant temperature	°C	MIU, DICE and ACC	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 the engine speed exceeds 650 rpm. The value is used by ACC and DICE.
CHECK ENGINE.	ON/OFF	MIU	ON, unit ON/OFF, is sent when the on-board diagnostics reports that the lamp is to be turned on. The value is used by MIU.
SHIFT UP	ON/OFF	MIU	ON, unit ON/OFF, is sent at low loads and high engine speeds and at very high engine speeds irrespective of load. The value is used by 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 MIU.
Fuel consumed since start	ml	MIU, SID	When the ignition is switched on, the value is 0 ml and is then accumulated for each injection, unit ml. The value is used by MIU.
Diagnostics		DICE/diagnostic tool	Trionic T7 responds to the diagnostics request from the diagnostic tool via DICE, no unit.