Bus communication
| Bus communication |
| P-bus and I-bus |
All the control modules in the Saab 9-5 are connected to the bus except those for the ABS and SRS.
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 data transfer rate on the P-bus is ten times faster than on the I-bus.
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 transmitted and varies between 10 milliseconds (0.010 seconds) and one second. Information is also sent out by the control modules whenever the information changes.
Information is transferred between control modules via two leads, BUS+ (green lead) and BUS- (white lead). On the P-bus, the leads are twisted to reduce their 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 control module can receive the immobilization information sent out by TWICE.
Permanent bus faults
All communication between Tech 2 and the bus-connected systems goes via DICE. Irrespective of which system is being contacted, Tech 2 and DICE will check to see that all the bus-connected systems in the car are activated and communicating. If any bus-connected control module is missing, Tech 2 will detect this. This means that all the bus-connected control modules are communicating correctly if there is no warning from Tech 2.Intermittent bus faults
The Trionic control module and the transmission control module (TCM) continuously check that all control modules from which they obtain information are communicating correctly. If intermittent faults occur in bus communication, diagnostic trouble codes will be generated in the Trionic and transmission control modules. The cause of the fault may be that the control module concerned has lost power or one of the bus leads is disconnected.Incorrect values on the bus
Diagnostic trouble codes are set in Trionic and TCM if any information they receive from the bus has an incorrect value. The trouble code readout will refer to the faulty system.For further information on the bus, see Bus and Diagnostics Communication.
| The main unit uses the following information |
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Information
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Unit
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Sensor system
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Description
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Ignition +B
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ON/OFF
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DICE
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The main unit uses the +B information only as logic voltage.
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Key Correct
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-
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DICE, TWICE
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The main unit uses the information for the theft protection function of the audio system.
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Diagnostics communication
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DICE
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For further information on the bus, see Bus and Diagnostics Communication.
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| The main unit transmits the following information |
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Information
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Unit
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User system
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Description
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Sound
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Acoustic information
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SID
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SID uses the information to activate the type of sound requested from the main unit.
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Text Message
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Text information
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SID
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SID uses the information to display the setting of the source currently in use.
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Diagnostics communication
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-
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DICE
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For further information on the bus, see Bus and Diagnostics Communication.
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