Bus communication
| Bus communication |
| P bus and I bus |
In the Saab 9-5, all the car's control modules are connected to buses with the exception of the ABS and SRS control modules.
The bus is divided into the power train (P bus) and the instrument bus (I bus). Both busses are connected to the main instrument display panel (MIU). The busses are electronically separated.
The P-bus has a data transfer rate ten times higher than that of the I-bus.
All the information that one control module sends is available to all the other control modules connected to the bus. The MIU is responsible for ensuring that all the information on one bus is also available on the other.
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.
The transfer of information between the control modules is achieved on two leads BUS+ (green lead) and BUS- (white lead). Both leads of the P-bus are twisted to increase the tolerance to electrical interference.
Diagnostics
In a bus system, all the units must be able to communicate with each other. For example, the engine cannot be started if Trionic is unable to receive immobilizer information from TWICE.Intermittent bus faults
Trionic and TCM check continuously to see that all the control modules they receive information from are communicating correctly. In the event of an intermittent fault occurring in the bus communication, diagnostic trouble codes will be set in Trionic and TCM. The cause of the fault can be that the power supply or one of the bus leads to the control module in question is absent.Permanent bus faults
All communication between the diagnostics tool and the bus-connected systems goes via DICE. Irrespective of which system is being contacted, the diagnostics tool and DICE will check to see that all the bus-connected systems in the car are activated and communicating. If any of the bus-connected control modules are missing, the diagnostics tool will detect this. This means that all the bus-connected control modules are communicating correctly if there is no warning from the diagnostics tool.Incorrect values on the bus
TRIONIC and TCM generate a diagnostic trouble code (DTC) when the information they fetch from the bus has an erroneous value. The text in the diagnostic trouble code refers to the system in which the error exists.| ACC uses the following information: |
| Information | Sensor system | ||||||||||||||||||||||||
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Electrically heated rear window,
confirmation (ON/OFF) |
DICE
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DICE sends electrically heated rear window ON/OFF. When ON, the button symbol appears on the display.
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Passenger seat Front,
Occupied (YES/NO) |
TWICE
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When YES, the control module will select the latest passenger temperature setting (the passenger must sit down before the speed exceeds 30 km/h for the first time).
If NO, the passenger side temperature setting will follow the driver's selection (ignition must have been turned off for more than 10 minutes). If any of the buttons on the passenger side should be pressed, the driver's selection is cancelled. |
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Vehicle speed,
left rear wheel (km/h) |
MIU
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MIU sends vehicle speed (km/h). The value is used to engage air recirculation at high outside temperatures and to filter the outside temperature from SID.
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Unit (Celsius, Fahrenheit)
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SID
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SID sends temperature unit (Celsius, Fahrenheit). The value is used to display selected temperature unit.
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Language (English, German, French, Spanish, Swedish)
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SID
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SID sends the selected language. The value is used to write text messages on SID in the selected language.
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Rheostat value (0-100%)
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SID
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SID sends the rheostat value (%). The value is used to regulate the brightness of the button background lighting.
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Rheostat value, Night Panel (0-100%)
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SID
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SID sends the rheostat value for Night Panel 0-100%. The value is used to regulate the button background lighting when Night Panel is ON.
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Night Panel (ON/OFF)
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SID
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SID sends Night Panel (ON/OFF). When ON, the display goes out.
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Display lighting (0-100%)
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SID
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SID sends display lighting value (%). The value is used to regulate the display background lighting.
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Time Engine Off (minutes)
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SID
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SID sends time engine off (minutes). The value is used to calculate current temperature at head height for the front seat passenger and driver. The following are also used as default values:
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Steering wheel location
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TWICE
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TWICE sends the steering wheel location (right/left). The value is used to decide which zone is the driver's zone.
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Outside temperature (°C)
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SID
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SID sends the outside temperature (°C). The value is used to calculate the temperature at head level for the front seat passenger and driver. Defaults values also used are:
The value is attenuated and filtered in the ACC unit and can therefore differ from that shown on the SID display. |
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Engine Has Started (ON/OFF)
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TRIONIC
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TRIONIC sends Engine Has Started (ON/OFF). When OFF and engine speed below 600 rpm, the fan current is limited to 5 A.
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Engine speed (rpm)
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TRIONIC
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TRIONIC sends engine speed (rpm). When engine speed is below 600 rpm and Engine Has Started is OFF, the fan current is limited to 5 A.
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Coolant temperature (°C)
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TRIONIC
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TRIONIC sends coolant temperature (°C). The value is used to calculate fan current and air distribution position for cold starts.
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Diagnostics
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DICE/
diagnostics tool |
The diagnostics tool sends a diagnostic request via DICE (no unit). The value is used to answer the current request.
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| ACC sends the following information: |
| Information | User System | ||||||
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Text message
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SID
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ACC sends Text message when extended user programming is activated/inactivated. The value is used by SID.
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Sound
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SID
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ACC sends Sound when extended user programming is activated/inactivated. The value is used by SID.
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A/C (ON/OFF)
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DICE
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ACC sends A/C (ON/OFF). ON is sent when ECON is not selected and the outside temperature exceeds 5°C and the fan speed is at least minimum speed. The value is used by DICE. Note that there are additional inhibitor conditions in DICE.
Note: As the outside temperature value is not allowed to rise unless the vehicle speed exceeds 30 km/h, A/C will not be requested if the outside temperature was below 5°C before the car was driven into the workshop (see activating: Outside temperature 20°C). |
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Rear window heater (ON/OFF)
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DICE
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ACC sends Rear window heater (ON/OFF). ON is sent when the rear window heater is turned on. The value is used by DICE.
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Diagnostics
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DICE/diagnostics tool
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ACC answers to the diagnostics request from the diagnostics tool via DICE (no unit).
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