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)

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MIU (540)

•

SID (541)

•	Control module, ABS (547)

•	Control module STC (565)

•	Control module, Trionic OBDII (589)

•	Control module EDC 15 (595)

•	Control module, extra heater (597)

•	Diesel pump (598)

•	Control module, DICE (628)

•	Control module, TWICE (632)

P bus and I bus

A "bus" in this context means cables through which information is sent digitally and serially. By digital is meant that the voltage difference between the cables has only two values, approx. 0 and 5 V. The information is coded so that different combinations of pulses with the values 0 and 5 V denote different things.

By serial is meant that the information is sent in express packages” one after the other in very fast succession.

In the Saab 9-3, half of the car's control modules are connected to the buses.

The buses consist of a P bus (Power-train 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 DICE, one of the control modules connected to the I bus, and has therefore access to all the control modules connected to the bus.

The data transfer rate on the P bus is ten times higher than the I bus. The reason for this is that the power-train systems cannot work properly unless information is transferred with the minimum possible delay.

All the information sent from one control module is accessible to all other control modules connected to 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.

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

DICE

DICE transmits	Values	Used by	The value depends on the following sensor input, signal or function
Position lights	ON/OFF	SID	Activation by control module of relay output for main lighting relay
Rear fog light broken	YES/NO	SID	Control module current measurement of output to lamp
LH direction indicators	ON/OFF	MIU, SID	Control module activation of output to lamps
RH direction indicators	ON/OFF	MIU, SID	Control module activation of output to lamps
Rear fog light	ON/OFF	MIU	Activation by control module of output to fog lights
Acoustic signal	Remind	SID	Control module programming and seat-belt buckle switches, driver's door or passenger's door open (bus from TWICE)
Ignition +B	ON/OFF	TWICE, Audio system	Ignition switch
Ignition +15	ON/OFF	--	Ignition switch
Ignition +54	ON/OFF	TWICE	Ignition switch

TWICE

TWICE transmits	Values	Used by	The value depends on the following sensor input, signal or function
LH rear light broken	YES/NO	SID	Control module current measurement of output to lamps
RH rear light broken	YES/NO	SID	Control module current measurement of output to lamps
LH rear light	ON/OFF	DICE	Control module input supplied with current from light switch
RH rear light	ON/OFF	DICE	Control module input supplied with current from light switch
LH brake light broken	YES/NO	SID	Control module current measurement of output to lamp
RH brake light broken	YES/NO	SID	Control module current measurement of output to lamp
High-level brake light broken	YES/NO	SID	Control module current measurement of output to lamp
Brake lights	ON/OFF	SID	Brake light switch
Acoustic signal	Sound information	SID	In connection with text message
Driver's door	OPEN/CLOSED	MIU,PSM DICE	Door switch
Passenger door	OPEN/CLOSED	MIU,PSM DICE	Door switch
LH rear door	OPEN/CLOSED	MIU, DICE	Door switch
RH rear door	OPEN/CLOSED	MIU, DICE	Door switch
Boot lid	OPEN/CLOSED	MIU, DICE	Lid switch
Diagnostics communication	--	DICE/diagnostic tool	Control module should be live and the bus leads intact

SID

SID transmits	Values	Used by	The value depends on the following sensor input, signal or function
Rheostat level	0 -100 %	Audio, ACC, DICE, MIU	Rheostat control module input
Rheostat Night Panel	0 -100 %	Audio, ACC, DICE, MIU	Rheostat control module input reduced internally by a fixed value
Night Panel	ON/OFF	Audio, ACC, DICE, MIU	Button
Diagnostics communication	--	DICE/diagnostic tool	Control module should be live and the bus leads intact