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 M2.10.3 (505)

•	Control module, ACS (509)

•

MIU (540)

•

SID (541)

•	Control module (ABS) 547

•	Control module, folding top opening (565)

•	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

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.

Half the control modules in the Saab 9-3 are connected to the bus.

The bus is divided into 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 directly 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 on the P-bus is ten times faster than on the I-bus. This is because the power train systems require information with as short a delay as possible.



All the information sent from one control module is accessible for all other control modules on the bus. The MIU is responsible for ensuring that information available on one bus is also available on the other bus.

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 information is transferred between control modules via two leads, bus+ (green lead) and bus- (white lead). The leads are twisted to reduce their sensitivity to electrical interference.

The MIU uses the following information:

Information	Unit	Sensor system	Description
LH direction indicators	ON/OFF	DICE	MIU turns on the indicator lamp for the LH direction indicators.
RH direction indicators	ON/OFF	DICE	MIU turns on the indicator lamp for the RH direction indicators.
Rear fog light	ON/OFF	DICE	MIU turns on the indicator lamp for the rear fog lights.
Driver's door	OPEN/CLOSED	TWICE	MIU lights the symbol for the driver's door.
Passenger door	OPEN/CLOSED	TWICE	MIU lights the symbol for the passenger door.
LH rear door	OPEN/CLOSED	TWICE	MIU lights the symbol for the LH rear door.
RH rear door	OPEN/CLOSED	TWICE	MIU lights the symbol for the RH rear door.
Boot lid	OPEN/CLOSED	TWICE	MIU lights the symbol for the boot lid.
Steering wheel location	LHD/RHD	TWICE	MIU turns on the indicator for the driver/passenger door
Immobilizer	ON/OFF	TWICE	Immobilizer function
Info Disp Lamp	ON/OFF	SID	MIU turns on the Info Display indicator lamp.
Rheostat level	0-100 %	SID	The main instrument unit controls the instrument lighting.
Night Panel	ON/OFF	SID	MIU turns off certain instrument and display lighting.
Display lighting	0-100 %	SID	MIU uses this information to control the display lighting.
Light intensity in compartment	Lux	SID	MIU uses this value to control the intensity of the indicator lamps.
CHECK ENGINE lamp	ON/OFF	EDC 15	MIU turns on the CHECK ENGINE lamp.
CRUISE Lamp	ON/OFF	EDC 15	MIU turns on the CRUISE lamp.
Fuel consumed since start	0-65535 ml	EDC 15	Used by SID for the trip computer functions, can be adjusted by an offset on MIU.
Engine speed	0-6000 rpm	EDC 15	MIU controls the tachometer.
Coolant temperature	-40-215°C	EDC 15	MIU control the coolant temperature gauge.
Glow indicator lamp	ON/OFF	EDC 15	The glow indicator lamp goes on during pre-heating.

The MIU sends the following information:

Information	Unit	Used by	Description
Vehicle speed	km/h (mph)	EDC 15, DICE, SID, ACC, Audio, TWICE, STC	The main instrument unit calculates the current vehicle speed based on information on the wheel speed from the ABS control module.
Sound	Sound information	SID	Request for acoustical signal when central warning lamp or Info Displ goes on.
Fuel level	litres	SID	MIU sends information on the current fuel volume in the tank.
Odometer reading	km, miles	SID	Information on the driven distance.
Identification number	---	TWICE	Immobilizer function
Diagnostics communication	---	DICE/ Diagnostic tool	DICE/diagnostic tool.
STOP FOR FUEL	Text message	SID	MIU sends the text message to SID, which shows it on the display.