Brief description of the main instrument unit
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Brief description of the main instrument unit
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The main instrument unit conveys information to the driver and functions as an information link between the P bus and the I bus.
The main instrument unit has its own diagnostics function and sets a diagnostic trouble code when a fault occurs.
The main instrument unit incorporates the following:
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Coolant temperature gauge
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Instrument and display lighting
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Warning and indicator lamps
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The main instrument unit receives information from its own sensors and also from other systems. The control module processes the information, which is used to control instruments and lamps. Certain information is put on the bus.
The car is fitted with an electronic speedometer which shows the actual speed. Information on the speed comes from the ABS control module. The left rear wheel sensor sends speed information to the ABS control module.
The main instrument unit's control module stores the distance driven and shows it on the odometer display. The display has a six-digit register which the control module updates continuously from 000000 to 999999 km (or miles). The tripmeter has a four-digit register which starts at 000.0 and runs to 999.9 km (or miles).
The electronic tachometer shows the current engine speed. It receives information on the engine speed continuously on the bus from Trionic. The display of engine speeds below 1100 rpm is damped to obtain a more stable reading.
The fuel gauge gives the driver information on how much fuel is left in the tank. It consists of a fuel gauge in the main instrument unit and a level sensor in the tank.
With less than 10 litres of fuel in the tank, the main instrument unit's control module switches over to measure fuel consumption. Information is received on the bus from Trionic. This gives a more accurate reading of the fuel level. The fuel reserve indicator lamp goes on when the fuel level is under 10 litres.
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Coolant temperature gauge
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The coolant temperature gauge gives the driver information on the engine coolant temperature. Information is received on the bus from Trionic.
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Warning and indicator lamps
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The main instrument unit contains the following lamps:
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Indicator lamp INFO DISPLAY, lights up when a message is shown on the SID unit.
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Central warning lamp, lights up when a fault occurs in a system having to do with the car's safety.
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Oil pressure warning lamp, warns the driver when engine oil pressure is too low.
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Charge warning lamp, indicates to the driver whether or not the generator is charging.
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AIRBAG warning lamp, warns the driver when a fault has occurred in the airbag system.
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The brake fluid warning lamp warns the driver if the level of the fluid in the reservoir is too low.
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Handbrake warning lamp, tells the driver that the handbrake is on.
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TCS indicator lamp, comes on when Traction Control System is active; found on cars with TCS.
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TCS OFF indicator lamp, comes on when Traction Control System is switched off or on a fault in the system; found on cars with TCS.
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ABS warning lamp, the lamp lights up when there is a fault in the ABS system.
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SPORT indicator lamp, on cars with automatic transmission indicates to the driver that the SPORT mode is active.
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WINTER indicator lamp, on cars with automatic transmission indicates to the driver that the WINTER mode is active.
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CHECK GEARBOX indicator lamp, warns the driver when there is a fault in the automatic transmission.
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Fuel reserve indicator lamp, the lamp lights up when the fuel level is below 10 litres.
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CHECK ENGINE indicator lamp, warns the driver that there is a fault in the engine management system.
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Direction indicator repeater lamps, right and left. Show when the direction indicators are on.
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CRUISE indicator lamp, on cars with cruise control the lamp lights up when cruise control is engaged.
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SHIFT UP indicator lamp, the lamp lights up when a higher gear should be engaged (certain markets).
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Lights-on indicator lamp, indicates that the headlamps are on.
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Rear fog light indicator lamp, indicates that the rear fog light is on.
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Main beam indicator lamp, indicates that the main beam is on.
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Selector lever position indicator, indicates the selected gear position on cars with automatic transmission.
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Door indication, indicates if any of the doors or the tailgate is open.
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Instrument and display lighting
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The main instrument unit's control module controls the instrument and display lighting according to the light intensity in the cabin in combination with the selected rheostat setting. This gives a good level of lighting for day or night driving and optimum bulb life.
All the control modules in the Saab 9-5 are connected to the bus except those for the ABS and SRS.
The bus is divided into a Powertrain bus (P bus) and an Instrument bus (I bus). Both buses are connected to the main instrument unit (MIU). The buses have separate electrical systems.
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.
