Bus communication
| Bus communication |
| P-bus and I-bus |
In the Saab 9-5, all the car's control modules are connected to the buses with the exception of the ABS and SRS control modules.
The buses are 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.
The P-bus has a data transfer rate ten times higher than that of the I-bus.
All information sent out 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 made available on the other.
The control module sends out information on the bus at regular intervals. The time between two transmissions depends on which information is being transmitted and varies between 10 milliseconds (0.010 secs.) and one second. Information is also sent out by the module whenever the information changes.
Information is transferred between the various control modules via two leads, BUS+ (green lead) and BUS- (white lead). On the p-bus the leads are twined together to reduce sensitivity to electrical interference.
| Diagnostics |
In a bus system, all units must be able to communicate with each other. For example, the engine cannot start unless the Trionic module can receive the immobilization information sent out by TWICE.
Permanent bus faults
All Tech 2 communication with systems connected to the bus takes place through DICE. Irrespective of which system is contacted, TECH 2 via DICE first checks that all on-board systems connected to the bus are turned on and communicating. If any module connected to the bus is missing, Tech 2 will show this. This means that all control modules connected to the bus can communicate correctly unless Tech 2 warns otherwise.Intermittent bus faults
The Trionic and TCM control modules always check that all modules from which they receive information are communicating properly. On an intermittent fault in the bus communication, DTCs will be given in the Trionic and TCM modules. The cause of the fault may be that the control module concerned has lost power or one of the bus leads has been disconnected.Incorrect values on the bus
A Diagnostic Trouble Code (DTC) is given in the Trionic and TCM modules if any information they obtain from the bus has an incorrect value. The DTC text indicates the system where the fault has occurred.For further information about the buses, see Bus and Diagnostic Communication
.
| TWICE uses the following information |
|
Information
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Unit
|
Sender system
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Description
|
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Vehicle speed
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km/h, mph
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MIU
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TWICE uses the information for automatic control of the locks by the central locking system.
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SID button
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Night Panel
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SID
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TWICE uses the information to disconnect the glass breakage sensor and tilt sensor. The Night Panel is used to do this with the key removed from the ignition.
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Ignition +54
|
ON/OFF
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DICE
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TWICE uses the information to report the ignition switch status for the functions, lamp check, seat belt warning, heated rear seat, and electric powered front seats.
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Outside temperature
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°C
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SID
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TWICE uses the information to control the rear seat heating.
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Diagnostic communication
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|
Tech 2
|
See Bus and diagnostics communication
|
| TWICE sends out the following information |
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Information
|
Unit
|
User system
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Description
|
|
Left rear light faulty
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YES/NO
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SID
|
SID uses the information to display the CHECK message.
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Right rear light faulty
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YES/NO
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SID
|
SID uses the information to display the CHECK message.
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Left rear light
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ON/OFF
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DICE
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DICE uses the information to calculate the position of the light switch.
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Right rear light
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ON/OFF
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DICE
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DICE uses the information to calculate the position of the light switch.
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Tailgate
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OPEN/CLOSED
|
DICE, MIU
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DICE uses the information to turn on the luggage compartment light.
MIU uses the information to turn on the display for open tailgate. |
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Left rear door
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OPEN/CLOSED
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DICE, MIU
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DICE uses the information to turn on the interior light.
MIU uses the information to turn on the display for open door. |
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Right rear door
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OPEN/CLOSED
|
DICE, MIU
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DICE uses the information to turn on the interior light.
MIU uses the information to turn on the display for open door. |
|
Brake lights
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ON/OFF
|
TCM, Trionic
|
TCM uses the information for engaging gear.
Trionic uses the information for the cruise control function. |
|
Left brake light faulty
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YES/NO
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SID
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SID uses the information to display the CHECK message.
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Right brake light faulty
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YES/NO
|
SID
|
SID uses the information to display the CHECK message.
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|
High level brake light faulty
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YES/NO
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SID
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SID uses the information to display the CHECK message.
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Driver's door
|
OPEN/CLOSED
|
DICE, MIU, PSM
|
DICE uses the information to turn on the interior light.
MIU uses the information to turn on the display for open door. PSM uses the information to control the function, electric powered front seat. |
|
Immobilization
|
ON/OFF
|
Trionic
|
Trionic uses the information to allow the engine to start.
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|
Sound
|
Sound information
|
SID
|
SID uses the information to generate sound for the seat belt warning function.
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|
Key correct
|
ON/OFF
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Audio
|
The audio system uses the information for anti-theft protection.
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Passenger door
|
OPEN/CLOSED
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MIU, PSM, DICE
|
DICE uses the information to turn on the interior light.
MIU uses the information to turn on the display for open door. PSM uses the information to control the function, electric powered front seat. |
|
Passenger seat occupied
|
YES/NO
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ACC
|
ACC uses the function for one or two zone control.
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|
Steering wheel position
|
LHD/RHD
|
PSM, ACC
|
PSM uses the information to know which door is the driver's door.
ACC uses the information to know which is the driver's zone. |
|
Horn
|
0: 6: 42 ms
|
SID
|
SID uses the information to activate the horn relay when the car is TSL locked.
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Test brake lights
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ON/OFF
|
SID
|
SID tells the driver via a CHECK message to press the brake pedal.
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Text message
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SID
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SID uses the information to display text messages for the TWICE functions.
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Hazard flashers
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ON/OFF
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DICE
|
DICE uses the information to activate the hazard flashers when the anti-theft alarm is tripped.
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Central locking system
|
LOCKED/UNLOCKED
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DICE
|
DICE uses the information to turn on the interior light when the car is unlocked.
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Diagnostics
|
|
Tech 2
|
See Bus and diagnostics communication
|
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