Bus communication

Bus communication

•	Trionic, engine management system (TRIONIC)

•	TCM (Transmission Control Module), control module for automatic transmission (502)

•	P-bus (Powertrain bus)

•	MIU (Main Instrument Unit) (540)

•	I-bus (Instrument bus)

•	SID (Saab Information Display) (541)

•	TWICE (Theft Warning Integrated Central Electronics) (632)

•	ACC (Automatic Climate Control) (216)

•	Audio system, main unit (353)

•	CDC (CD changer) (355)

•	PSM (Power Seat Memory) (357Dk)

•	PMM (Power Mirror Memory) (611)

•	DICE (Dashboard Integrated Central Electronics) (628)

•	Data link connector (H16-5/445)

•	Airbag (SRS) (331)

•	ABS (Anti Block System) (547)/TC-ABS (382)

P-Bus and I-Bus

A bus is understood to be the leads over which information is sent digitally and serially. Digital means that the voltage difference between the leads has only two values, roughly 0 V and 5 V. The information is coded so that different combinations of 0 V and 5 V pulses have different meanings.

Serial means that the information is sent in ”packets” which are transmitted one after the other in rapid succession.

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 consist of a P-bus (Powertrain Bus) and an I-bus (Instrument Bus). Both buses are connected to the MIU (Main Instrument Unit). The buses are electrically isolated from each other.

The diagnostic tool is not connected direct to the bus but communicates via the DICE, one of the control modules connected to the I-bus, and so has access to all control modules connected to the bus.

The data transfer rate of the P-bus is ten times faster than that of the I-bus. The reason for this is that the powertrain systems need information with the least possible delay, as for example when providing air mass compensation when the selector lever is moved from N to D or torque limitation in connection with gear changing.

All information sent out on a bus 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 modules send out 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 1 second. Information is also sent out by the control modules whenever the information changes.

The transfer of information between control modules takes place on two leads, bus+ (green lead) and bus- (white lead). The leads are twisted to reduce susceptibility to electrical interference.

SID uses the following information

Information	Values	From	The value depends on the following sensor input, signal or function
Position light	ON/OFF	DICE	Right rear light or Left rear light (bus value from TWICE). The SID uses the information when calculating the rheostat value.
Rear fog light broken	YES/NO	DICE	Control module current measurement of output to lamp. The SID uses the information for CHECK messages.
LH direction indicators	ON/OFF	DICE	Control module activation of output to lamps. The SID activates TICK-TACK for the direction indicator function.
RH direction indicators	ON/OFF	DICE	Control module activation of output to lamps. The SID activates TICK-TACK for the direction indicator function.
Sound	Acoustic information	DICE, TWICE, ACC, Audio, MIU, PSM	The SID activates the type of sound that has been requested via the bus.
Left rear light broken	YES/NO	TWICE	Control module current measurement of output to lamp. The SID uses the information for CHECK messages.
Right rear light broken	YES/NO	TWICE	Control module current measurement of output to lamp. The SID uses the information for CHECK messages.
LH brake light faulty	YES/NO	TWICE	Control module current measurement of output to lamp. The SID uses the information for CHECK messages.
RH brake light faulty	YES/NO	TWICE	Control module current measurement of output to lamp. The SID uses the information for CHECK messages.
High-level brake light faulty	YES/NO	TWICE	Control module current measurement of output to lamp. The SID uses the information for CHECK messages.
Brake lights	ON/OFF	TWICE	Brake lights switch.
Test brake lights	ON/OFF	TWICE	Control module programming and brake lights switch. The SID sends the driver information via a CHECK message to depress the brake pedal. (Certain markets)
Horn	0 : 6 : 42 ms	TWICE	Anti-theft alarm function and central locking system function. The SID uses the information from TWICE and activates the horn for the requested time in ms as acknowledgement of “TSL” locking.
Text message	Text information	TWICE, ACC, Audio, Trionic, TCM	Anti-theft alarm function and central locking system function. Text information from TWICE concerning the anti-theft alarm function, from the ACC concerning user programming, the audio display and high transmission fluid temperatures.
RDS time	Hours, minutes, seconds	Audio	RDS reception. The SID uses the information for the time function (the clock).
RDS date	1-31	Audio	RDS reception. The SID uses the information for the time function (the clock).
RDS month	January - December	Audio	RDS reception. The SID uses the information for the time function (the clock).
Vehicle speed	km/h, mph	MIU	Rear left wheel speed. The SID uses the information for calculations for the trip computer function.
Fuel level	litres	MIU	Tank sensor, control module adjustment. The SID uses the information for calculations for the trip computer function.
Odometer reading	km, miles	MIU	Display value. The SID uses the information for calculations for the trip computer function.
Fuel consumed since start	0- 65535 ml	Trionic	Fuel injection function. The SID uses the information for calculations for the trip computer function.
Engine Started	ON/OFF	Trionic	Crankshaft position sensor. The SID uses the information to calculate “Engine off time”.
Coolant temperature	-40 - 215°C	Trionic	Coolant temperature. The SID uses the information for calculations for the trip computer function.
Diagnostics communication		DICE	Control module should be live and the bus leads intact. See Bus and diagnostics communication.

The SID sends out the following information

Information	Values	Used by	The value depends on the following sensor input, signal or function
Info Disp Lamp	ON/OFF	MIU	In connection with text message. The MIU lights the lamp on request from the SID.
Unit	Metric, Imperial (°F), Imperial (°C), US	ACC	The unit that has been selected with the button.
Language	English, German, French, Italian, Swedish, Spanish	ACC	The language that has been selected with the button. The SID transmits information about which language has been selected.
Steering wheel controls	VOL -, VOL +, SRC, SEEK >>, << SEEK, NXT	Audio	Button control module input. The SID send out information when a button is pressed (activated) on the steering wheel controls. Applies if the car has the Saab Audio System.
Rheostat level	0- 100%	Audio, ACC, DICE, MIU	Rheostat control module input. The SID transmits the data for regulating instrument and control lighting.
Rheostat Night Panel	0- 100%	Audio, ACC, DICE, MIU	Rheostat control module input reduced internally by a fixed value. Used for button illumination.
Night Panel	ON/OFF	Audio, ACC, DICE, MIU	Button. The Night Panel function is activated and deactivated.
Display lighting	0- 100%	ACC, MIU	Lighting level for all displays. The highest value of the rheostat control module input or light sensor.
Light intensity in the car	Lux	MIU	Light sensor. Used by the MIU to control the intensity of indicator lamps.
Engine Off Time	Minutes	ACC	+15. The ACC uses the value to calculate the settings when starting.
Outside temperature	°C	ACC, TWICE, DICE	Outside temperature sensor, control module adjustment. The SID transmits information for use by other systems.
Diagnostics communication	-	DICE	Control module should be live and the bus leads intact. See Bus and diagnostics communication.