Bus messages

/ 9-3 (9400) / 2003 / 3. Electrical System / Main instrument unit / Technical description / Bus messages

Bus messages

P bus and I bus

A bus is understood to be the leads over which information is sent digitally and serially. Digital means that the voltage difference between the leads has only two values, roughly 0 V and 5 V. The information is coded so that different combinations of 0 V and 5 V pulses have different meanings.

Serial means that the information is sent in ”packets” which are transmitted one after the other in rapid succession.

The bus is divided into the P-bus (Powertrain Bus) and the I-bus (Instrument Bus). Both buses are connected to the main instrument unit (MIU). The buses are electrically isolated from each other.

The control module for the airbag and SRS are not connected to the bus. The TC/ABS control module on cars with Traction Control is connected to the P-bus.

The diagnostic tool is not directly connected to the bus but communicates via DICE, which is connected to the I-bus, and therefore has access to all the control modules connected to the bus.

The P-bus has a data transfer rate ten times higher than that of the I-bus. This is because the P-bus requires information with the least possible delay.

All the information sent from one control module is accessible to all the other control modules on the bus. The MIU is responsible for making information on one bus 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 transmitted by the control module whenever the information changes.

The transfer of information between control modules takes place on two leads, bus+ (green lead) and bus- (white lead). The leads are twisted to increase their resistance to electrical interference.

The MIU uses the following information:

Information	Values	From	The value depends on the following sensor input, signal or function
Left Direction Indicator	ON OFF	DICE	Control module activation of output to lamps The MIU lights the indicator lamp for LH direction indicators.
Right Direction Indicator	ON OFF	DICE	Control module activation of output to lamps The MIU lights the indicator lamp for RH direction indicators.
Rear Fog Light	ON OFF	DICE	Control module activation of output to fog light The MIU lights the indicator lamp for the rear fog light.
Door Driver	OPEN CLOSED	TWICE	Door switch The MIU lights the driver's door symbol.
Door Passenger (Bus from TWICE)	OPEN CLOSED	TWICE	Door switch The MIU lights the passenger's door symbol.
LH rear door	OPEN CLOSED	TWICE	Door switch The MIU lights the LH rear door symbol
RH rear door	OPEN CLOSED	TWICE	Door switch The MIU lights the RH rear door symbol.
Trunk (Bus from TWICE)	OPEN CLOSED	TWICE	Lid switch The MIU lights the boot lid symbol.
Steering Wheel Position	Left Hand Drive (LHD) Right Hand Drive (RHD)	TWICE	Control module programming. MIU uses the information to indicate an open door on the pictogram, driver/passenger door.
Information Display Lamp	ON OFF	SID	The MIU lights the Info Display indicator lamp in the event of a text message.
Rheostat Value	0-100 %	SID	Rheostat control module input The MIU uses information on the rheostat setting to control the brightness of the instrument lighting.
Rheostat Night Panel, Filtered	0-100 %	SID	Rheostat control module input reduced by a fixed value.
NIGHT PANEL	ON OFF	SID	The MIU turns off the lighting of certain instruments and displays.
Display Lighting	0-100 %	SID	The MIU uses the information to control the display lighting.
Light intensity in cabin	lux	SID	The MIU uses the information to control the brightness of indicator lamps.
CHECK ENGINE Light	ON OFF	ECM	Internal diagnosis.
SHIFT UP Lamp	ON OFF	ECM	Wheel speed, front right (wire from ABS)
CRUISE Lamp	ON OFF	ECM	Cruise Control function
Turbo Gauge	0-255, no unit	ECM (petrol)	Current air mass per combustion.
Fuel Used	0-65535 ml	ECM	Fuel injection function.
Engine RPM	0-7000 rpm	ECM	Crankshaft position sensor
Coolant temperature	-40-215°C	ECM	Coolant temperature sensor
Glow indicator lamp	ON OFF	ECM (diesel)	Coolant temperature sensor
Selector lever Position	P, R, N, D, 3, 2, 1	TCM	Selector lever position sensor.
CHECK GEARBOX Lamp	ON OFF	TCM	Internal diagnosis.
SPORT	ON OFF	TCM	The button and oil temperature sensor and not limp-home or WINTER
WINTER	ON OFF	TCM	The button and oil temperature sensor and not limp-home
Wheel speed RL	0-300 km/h	TC/ABS	Wheel speed sensor RL
ABS lamp	ON/OFF	TC/ABS	Internal diagnostics
TCS OFF lamp	ON/OFF	TC/ABS	Switch, internal diagnostics
TCS lamp	ON/OFF	TC/ABS	Traction Control
Diagnostics communication	---	DICE/ Diagnostic tool	Control module should be live and the bus leads intact.

The MIU sends the following information:

Information	Values	Used by	The value depends on the following sensor input, signal or function
Vehicle speed	km/h mph	DICE, SID, ACC, Audio TWICE, STC, ECM	Wheel speed, rear left (wire from ABS, bus from TC/ABS). MIU controls the speedometer
Acoustic warning	Acoustic information	SID	Request for acoustic signal when central warning lamp or Info Displ goes on.
Fuel Consumed Since Start	0-65535 ml	SID	Bus from ECM. The reading is corrected by an adjustment factor in the MIU. The factor can be adjusted with the diagnostic tool.
Fuel level	Litres	SID	Tank sensor, control module adjustment The MIU sends information on the current amount of fuel in the tank.
Stop for fuel	Litres	SID	Tank sensor, control module adjustment The MIU sends information on the current amount of fuel in the tank.
Odometer reading	km miles	SID	Display value Information on distance driven.
Identification number	---	TWICE	The number is generated in the MIU when the immobilization code is programmed in TWICE.
Diagnostics communication	---	DICE/ Diagnostic tool	Control module should be live and the bus leads intact.

Bus messages

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