Functional Cluster
General
The instrument cluster contains indicator/display instruments, indicator lamps and an LCD module (display unit).
Coding data which determine the scope of functions of the instrument cluster are stored in a non-volatile data memory (data is retained when supply voltage is disconnected).
The various scope of functions include, for instance, the vehicle model and the country variant.
At present, there are four different country variants.
- ECE
- USA/Canada
- Gulf
Indicator/Display Instruments
The scope of indicator and display instruments in the instrument cluster differs depending on the vehicle model.
Depending on the vehicle model, the instrument cluster is equipped with an analog clock or a tachometer.
In the vehicle models of BMW Motorsport GmbH (M3), the fuel consumption indicator (KVA) is replaced by an engine oil temperature gauge.
Scope of Functions
Speedometer
Depending on the vehicle model, the instrument cluster is equipped with different speedometers. At present, two different speedometers are installed, each speedometer available in kilometers (220 km/h, 260 km/h) or miles (140 mph, 160 mph).
The instrument cluster receives the position signal tw from the rear axle reed contact (position signal sensor) and uses this signal to control the speedometer, odometer and trip odometer displays. The instrument cluster also makes available a position signal (speed-A) for the connected control units.
Tachometer
Depending on the vehicle model, the instrument cluster is equipped with different tachometers and different display ranges.
The engine speed signal (TD signal) comes from the engine control unit (DME or DDE) and, depending on the vehicle model, supplies a different number of pulses per crankshaft revolution.
The instrument cluster determines the indicated engine speed from the number of pulses per crankshaft revolution and the coded data stored in the instrument cluster.
Engine Speed Signal
The instrument cluster uses the engine speed signal not only to indicate the engine speed. The engine speed signal is also used for fuel consumption gauge, for the activation function of the excess temperature warning lamp in the coolant temperature gauge and for the activation function of the coolant temperature gauge.
Coolant Temperature
Together with the coolant temperature sensor, the instrument cluster determines the current coolant temperature. The coolant temperature sensor is a temperature-dependent resistor which is connected by means of two wires to the instrument cluster.
The voltage drop caused by the coolant temperature sensor is evaluated by the instrument cluster and indicated as a temperature on the basis of the stored coding data.
The temperature last stored is indicated in order to prevent the displayed temperature increasing when the ignition is switched on and the engine is stationary (post-heating phase and no engine speed signal from the engine control unit). If the calculated value is lower than the temperature last stored, then this value is indicated.
If the instrument cluster registers that the engine is running and the calculated temperature is greater than the value last stored, the coolant temperature gauge is switched for approx. 20 s to the current value.
Coolant Excess Temperature Warning Lamp
The warning lamp is activated by the instrument cluster when the excess temperature threshold is reached. The excess temperature threshold stored in the instrument cluster is 115 °C at *D* software number 11.0 and 125 °C from *D* software number 12.0.
Tank Content
The tank contents are measured by means of two series connected lever sensors. The lever sensor values, the fuel consumption signal tKVA and the data stored in the coding area of the instrument cluster are used to determine the tank contents.
Fuel Reserve Warning Lamp
The determined tank content are compared with the reserve threshold. If the determined value drops below this threshold value, the fuel reserve warning lamp is activated. The threshold value for the fuel reserve warning lamp is at 8 litre.
The values of the two lever sensors and the fuel consumption signal tKVA are monitored by the instrument cluster. If the indicated value is outside the value range of the two lever sensors and the fuel consumption signal is detected as defective, the fuel gauge is set to zero and the fuel reserve warning lamp is not activated.
Tank Content Signal to the On-Board Computer
The instrument cluster informs the on-board computer of the tank contents by way of an information signal as soon as terminal R "ON" is detected.
The value 0 liters is transferred if the tank sensors and the fuel consumption signal tKVA are found to be defective.
Fuel Consumption Signal tKVA
The fuel consumption signal tKVA is derived from the injection signal t1 from the digital motor electronics DME or from the measured signal injection quantity TQ from the digital diesel electronics DDE.
The indicated fuel consumption (quantity of fuel per unit distance covered) is calculated from the tKVA signal, the number of cylinders of the engine, the engine speed and the road speed.
Total and Trip Mileage (Distance Covered)
The instrument cluster controls the total and trip odometer with the rear axle reed contact (position signal sensor).
The total mileage is stored in a non-volatile memory (data is retained when supply voltage is disconnected).
The trip mileage is stored for as long as a voltage is supplied. The trip odometer is set to zero if the supply voltage is interrupted (battery disconnected) or the supply voltage is too low.
Instrument Lighting
The indicator/display instruments of the instrument cluster are illuminated by three lamps. Their brightness is controlled by the dimmer for the vehicle gauges.
The dimmer supplies a square-wave frequency whose pulse/pause ratio (pulse width modulation) can be set.
LCD Module
The total mileage odometer, trip odometer, the distance unit km or miles and the service interval indicator are displayed in the LCD module.
To control LC display, the position of the dimmer is linked to the brightness information of the photo-electric sensor and the background of the LC display is correspondingly illuminated.
Seat Belt Warning
A seat belt warning facility is presently provided for the country variants USA, Canada and Gulf States. The seat belt warning consists of a display symbol in the instrument cluster and an audible signal. If installed, a gong is also activated as part of the seat belt warning. If no gong is installed and the belt warning is activated, an acoustic generator installed in the instrument cluster is switched on.
The coding data determine the components to be activated. The seat belt warning is triggered by the buckle contact with the ignition switch in position "2" (terminal 15 ON).
Gong
The gong is activated by a square-wave signal. The frequency of the square-wave signal determines the tone frequency. The length of the tone is determined by the pause duration (signal to ground potential).
Brake Pad Wear
The brake pad wear symbol lights up when the brake pad sensor is interrupted. The indication remains on until the ignition is switched off. The indication is no longer activated after the ignition is switched on and the brake at the brake pad sensor is rectified for the first 30 seconds after switching on the ignition.
Transmission Fault / Transmission Oil Temperature
The EGS control unit informs the instrument cluster of the transmission oil temperature by way of an information signal. Information is no longer transferred if the EGS control unit detects a defect which results in restricted operation (substitute program). In this case, the voltage on this information line is no longer temporarily switched to ground. In this way, the instrument cluster detects that there is a fault in the transmission and consequently activates the EGS fault indicator.
The EGS fault indicator is also actuated when the information line from the EGS control unit to the instrument cluster has a break. In this case, no defect code is stored b the instrument cluster. The instrument cluster only detects a defect when the information signal is constantly switched to ground.