Bus communication
| Bus communication |
| P-bus and I-bus |
All the control modules in the Saab 9-5 are connected to the buses 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 unit sends out information on the bus at regular intervals. The time between two transmissions depends on what information is 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.
Information is transmitted between control modules on two leads, BUS+ (green lead) and BUS- (white lead). Both P-bus leads are twinned to decrease 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 immobilizer information emitted 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 always check that all control modules from which they obtain information are communicating properly. 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 its power supply or that 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
| TWICE uses the following information for the theft protection |
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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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SID buttons
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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 button is used to disconnect these when the key is out of the ignition.
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Diagnostics communication
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Tech 2
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See Bus and diagnostics communication
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| TWICE sends the following information for the theft protection |
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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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Immobilizer
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ON/OFF
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Trionic
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Trionic uses the information to allow the engine to start.
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Text message
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SID
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SID uses the information to show the text message for the theft protection.
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Key correct
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ON/OFF
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Audio
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The audio system and CD changer use the information for the audio system theft protection.
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Diagnostics
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Tech 2
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See Bus and diagnostics communication
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