System Overview

System Overview





^ Main instrument unit (540)
^ Engine oil pressure sensor (44)
^ Switch, handbrake (43)
^ Generator (2)
^ Level switch, brake fluid (42)
^ Level sensor, fuel (46)
^ ABS Control module (547)
^ SRS/Airbag control module (331)

Main Components





Brief Description Of The Main Instrument Unit

General
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:
^ Control module
^ Speedometer
^ Tachometer
^ Odometer/tripmeter
^ Fuel gauge
^ Coolant temperature gauge
^ Instrument and display lighting
^ Warning and indicator lamps

Control module
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.

Speedometer
The car is equipped with an electronic speedometer that displays the current vehicle speed. Vehicle speed information comes from the ABS or TC/ABS control module. The rear left wheel sensor sends vehicle speed information to the ABS or TC/ABS control module.

Odometer/tripmeter
The main instrument unit control module stores the driven distance and displays it on the odometer. The odometer display contains a 6-digit register that is continuously updated from 000000 to 999999 km (or miles). The tripmeter contains a four digit register starting at 000.0 and running to 999.9 km (or miles)

Tachometer
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.

Fuel gauge
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.

Coolant temperature gauge
The coolant temperature gauge gives the driver information on the engine coolant temperature. Information is received on the bus from Trionic.

Warning and indicator lamps
The main instrument unit contains the following lamps:
^ Indicator lamp INFO DISPLAY, lights up when a message is shown on the SID unit.
^ Central warning lamp, lights up when a fault occurs in a system having to do with the car's safety.
^ Oil pressure warning lamp, warns the driver when engine oil pressure is too low.
^ Charge warning lamp, indicates to the driver whether or not the generator is charging.
^ AIRBAG warning lamp, warns the driver when a fault has occurred in the airbag system.
^ The brake fluid warning lamp warns the driver if the level of the fluid in the reservoir is too low or if a fault has occurred in the ABS system.
^ Handbrake warning lamp, tells the driver that the handbrake is on.
^ ABS warning lamp, the lamp lights up when there is a fault in the ABS system.
^ SPORT indicator lamp, on cars with automatic transmission indicates to the driver that the SPORT mode is active.
^ WINTER indicator lamp, on cars with automatic transmission indicates to the driver that the WINTER mode is active.
^ CHECK GEARBOX indicator lamp, warns the driver when there is a fault in the automatic transmission.
^ Fuel reserve indicator lamp, the lamp lights up when the fuel level is below 10 litres.
^ CHECK ENGINE indicator lamp, warns the driver that there is a fault in the engine management system.
^ Direction indicator repeater lamps, right and left. Show when the direction indicators are on.
^ CRUISE indicator lamp, on cars with cruise control the lamp lights up when cruise control is engaged.
^ SHIFT-UP indicator lamp, the lamp lights up when a higher gear should be engaged (certain markets).
^ Lights-on indicator lamp, indicates that the head lamps are on.
^ Rear fog light indicator lamp, indicates that the rear fog light is on.
^ Main beam indicator lamp, indicates that the main beam is on.
^ Selector lever position indicator, indicates the selected gear position on cars with automatic transmission.
^ Door indication, indicates if any of the doors or the tailgate is open.

Instrument and display lighting
The main instrument unit's control module controls the instrument and display lighting according to the light intensity in the cabin combination with the selected rheostat setting. This gives a good level of lighting for day or night driving and optimum bulb life.

P-bus and I-bus





All control modules in the Saab 9-5 are connected to the bus with the exception of ABS and SRS. For cars with Traction Control, the TC/ABS control module is connected to the bus.

The bus allows large quantities of data to be sent between the control modules on only two cables. The bus is divided into a Powertrain bus (P-bus) and an Instrument bus (I-bus).

Trionic, TCM and TC/ABS power train systems require fast data communication so that no noticeable delay occurs, e.g. for torque limitation when changing gears.

Trionic, TCM and TC/ABS are connected to the P-bus, on which data transfer is ten times faster than on the I-bus.

The P-bus and I-bus are connected to the MIU. The MIU is responsible for making information on one bus available to the other bus.

The diagnostic instrument is not connected directly to the bus but communicates via the DICE, one of the control modules connected to the I-bus, and so has access to all control modules connected to the bus.

Vehicle speed data is important for many control modules. Since the ABS is not connected to the bus, the vehicle speed signal is sent on a separate lead from the ABS to the MIU. The MIU then sends the data over the busses. In cars with Traction Control, the TC/ABS sends vehicle speed data to the MIU via the P-bus.