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)

•

MIU (540)

•

SID (541)

•	Control module (ABS) 547

•	Control module STC (565)

•	Control module, Trionic OBDII (589)

•	Control module EDC 15 (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 a number of wires on which information is sent digitally and serially. Digital means that the voltage difference between two wires has only two values, about 0V or 5V. The information is coded so that different combinations of pulses with values 0V and 5V have different meanings.

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

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

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

The diagnostics instrument is not directly connected to the bus but communicates via DICE, which is connected to the I-bus, and therefore has access to all the control modules connected to the bus.

The P-bus has a data transfer rate ten times higher than that of the I-bus. This is because the P-bus requires information with the least possible delay.

All the information sent from one control module is accessible for all the other control modules on the bus. The MIU is responsible for making information on one bus available to 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 transmitted and varies between 10 milliseconds (0.010 seconds) and one second. Information is also transmitted by the control module 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.

DICE uses the following information

Information	Values	From	The value depends on the following sensor input, signal or function
LH rear lights	ON/OFF	TWICE	Control module current measurement of output to lamps. DICE uses the information for the instrument lighting, acoustic warning and rear fog lights.
RH rear lights	ON/OFF	TWICE	Control module current measurement of output to lamps. DICE uses the information for the instrument lighting, acoustic warning and rear fog lights.
Driver's door	OPEN/CLOSED	TWICE	Door switch DICE uses the information to turn on or off the interior lighting, for the visual warning and for the “Follow me home” function.
Passenger door	OPEN/CLOSED	TWICE	Door switch DICE uses the information to turn on or off the interior lighting, for the visual warning and for the “Follow me home” function.
Rear door, Left	OPEN/CLOSED	TWICE	Door switch DICE uses the information to turn on/off the interior lighting.
Rear door, Right	OPEN/CLOSED	TWICE	Door switch DICE uses the information to turn on/off the interior lighting.
Boot lid	OPEN/CLOSED	TWICE	Lid switch DICE uses the information to turn on/off the luggage compartment lighting.
Hazard flashers	ON/OFF	TWICE	Anti-theft alarm function and central locking system function DICE uses the information to activate/deactivate the hazard flashers for the car's anti-theft alarm.
Central locking system	UNLOCKED/LOCKED	TWICE	Central locking system function DICE uses the information to turn off/on the interior lighting.
A/C	ON/OFF	ACC	AUTO selected and outside temperature (bus from SID) DICE uses the information to activate/deactivate the car's radiator fan and A/C systems.
Rear Window Heater	ON/OFF	ACC	Button on dashboard DICE uses the information to activate/deactivate the heating.
Vehicle speed	km/h, mph	MIU	Rear left wheel speed (lead from ABS) DICE uses the information for the intermittent windscreen wiper operation and for controlling the car's radiator fan and A/C systems.
A/C Relay	ON/OFF	MIU	Lead from Trionic or Motronic DICE uses the information to activate/deactivate the car's radiator fan and A/C systems.
Engine coolant temperature (Not Diesel)	-40 - 215°C	MIU	MIU has its own engine coolant temperature sensor on cars with petrol engine. DICE uses the information to control the radiator fan and A/C systems.
Rheostat level	0-100 %	SID	Rheostat control module input. DICE uses the information to control the brightness of the instrument and control lighting.
Rheostat Night Panel	0-100 %	SID	Rheostat control module input reduced internally by a fixed value. DICE uses the information to control the brightness of the buttons when NIGHT PANEL is active.
Night Panel	ON/OFF	SID	Button DICE uses the information on whether NIGHT PANEL is activated or deactivated.
Outside temperature	°C	SID	Outside temperature sensor, control module adjustment DICE uses the information to control the car's radiator fan and A/C systems.
Engine Running	ON/OFF	EDC 15	Crankshaft position sensor DICE uses the information to control the car's radiator fan and A/C systems.
Coolant temperature	-50 - 200°C	EDC 15	Coolant temperature sensor DICE uses the information to control the radiator fan and A/C systems.
Diagnostics		DICE/Diagnostic tool	Control module should be live and the bus leads intact. See Bus and diagnostics communication

DICE sends the following information

Information	Values	Used by	The value depends on the following sensor input, signal or function
A/C	ON/OFF	MIU, EDC 15	A/C (bus from ACC), coolant temperature (bus from Trionic), A/C pressure and evaporator temperature. Trionic and EDC 15 use the information to control relays.
A/C Pressure	bar	EDC 15	A/C pressure sensor EDC 15 uses the information for load compensation.
Current consumption	A	MIU	Control module activation of the relay outputs for the radiator fans and the electrically heated rear window. Trionic uses the information for load compensation.
Position lights	ON/OFF	SID	Control module activation of the relay output for the headlamp relay. SID uses the information for the instrument lighting functions.
Electrically heated rear window	ON/OFF	ACC	Control module activation of the relay output for the electrically heated rear window. ACC uses the information to confirm that the rear window heating is active.
Rear fog light defective	YES/NO	SID	Control module current measurement of output to lamp. SID uses the information to display a CHECK message.
Left Direction Indicator	ON/OFF	MIU, SID	Control module activation of output to lamps. MIU uses the information to indicate activated LH direction indicators with the control lamp on the main instrument unit SID uses the information for acoustic indication of activated direction indicators “tick-tack”.
Right Direction Indicator	ON/OFF	MIU, SID	Control module activation of output to lamps. MIU uses the information to indicate activated RH direction indicators with the control lamp on the main instrument unit. SID uses the information for acoustic indication of activated direction indicators “tick-tack”.
Rear Fog Light	ON/OFF	MIU	Control module activation of output to fog light. MIU uses the information to turn on/off the rear fog light indicator on the main instrument unit.
Sound	Acoustic information	SID	Control module programming and seat-belt buckle switches, driver's door or passenger's door open (bus from TWICE). SID uses the information to generate acoustic warnings.
Ignition +B	ON/OFF	Audio, TWICE	Ignition switch Informs Audio and TWICE of the position of the ignition switch.
Ignition +15	ON/OFF	TWICE	Ignition switch Informs TWICE of the position of the ignition switch.
Ignition +54	ON/OFF	TWICE	Ignition switch Informs TWICE of the position of the ignition switch.
Ignition +50	ON/OFF	TWICE, ACC	+15 present but not +54. Informs TWICE and ACC of the position of the ignition switch.
Diagnostics		DICE/Diagnostic tool	Control module should be live and the bus leads intact. See Bus and diagnostics communication