Base Instrument Cluster
The base instrument cluster consists of five analog gauges. The processing electronics and drivers for the gauges are contained in the cluster. The five gauges include
Scheme 198
- Fuel Gauge.
- Speedometer.
- Tachometer.
- Fuel Economy Gauge.
- Coolant Temperature.
Three Liquid Crystal Display blocks are provided for the
- Check Control Display - pictogram.
- Mileage, Outside Temperature and BC Display.
- Transmission Range and SI Display.
Warning lamps and indicators are positioned to the left and right of the display blocks. The number of warning lamps is greater on the base cluster for the display of several check control warnings. All of the warning lamps and indicators are LEDs and not replaceable. Critical warning lamps use two LEDs for a safety margin.
There are replaceable lamps for the back lighting on the liquid crystal display units.
The LEFT DISPLAY BLOCK contains a pictogram for various check control warnings. LEDs within the display will illuminate for
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- Lighting failures for headlight (low beam), taillight and brake lights.
- Open doors or trunk.
- Low washer fluid.
Additional circuits monitored by check control include the engine oil level and transmission emergency program. These warnings are indicated by lamps positioned in both indicator display areas on the left and right sides on the bottom of the instrument cluster.
Due to the ability to illuminate multiple warning LEDs, there is no priority displays for the pictogram check control. If multiple faults exist, each corresponding LED will illuminate.
The LED will remain illuminated as long as the fault exists. The only exception is the washer fluid which will go out 60 seconds after KL 15 is switched ON.
All check control and lamp control circuits are monitored by the Light Check Module (LCM). When failures or faults exist, the messages are passed to the cluster for display over the K-Bus.
The MIDDLE BLOCK contains the displays for the Total Mileage, Trip Mileage and Board Computer.
The total mileage is stored in non-volatile memories in the cluster EEPROM and the LCM.
The mileage can be displayed with the key off for 25 seconds if the mileage reset button is pressed.
Scheme 200
Board Computer information can be displayed by pressing the turn signal lever.
The RIGHT BLOCK contains the displays for the automatic transmission driving range and the Service Interval Indicator III.
The display of the Service Indicator on the E39 is the same as the "High" clusters. The processor for the intervals is located in the cluster electronics. The processing method for determining interval times uses the Service Interval III system. Interval times are based on fuel consumption instead of mileage and starts. This system was introduced on the 1996 E38 - 750iL.
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Using fuel consumption offers several advantages over the SIA II method for determining oil service.
- First, the processing electronics are less involved in that only one value is needed for the processing.
- Second, the use of fuel consumption is a more accurate method of determining engine load and the need for service.
- Third, resetting of the indicator before the scheduled time will not effect the time to the next service.
A set volume of fuel (in liters) is stored in the EEPROM of the SI. The volume of fuel is dependent on the vehicle and engine size. The processor receives the "ti" signal as the vehicle is used. As 20% of the stored volume is consumed, one of the green LEDs will go out. Each successive 20% of fuel consumption will cause the next LED to go out until 100% of the stored volume has been consumed. At this point the yellow LED will come on indicating the service is due. At 108% of the volume, the RED LED will illuminate indicating an over due service.
With each reset (oil service ore inspection), the total volume of fuel is restored in the EEPROM and the calculation starts over again.
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Distance Signal- This input is supplied to the cluster by the ASC/DSC control module as a square wave signal. Pulses from the left rear wheel speed sensor are processed by the DSC module to produce this signal. The cluster electronics process the input for the cluster display and pass the signal along on the K bus as speed signal "A" for other control modules requiring the vehicle speed signal.
Engine Control Module Signals - The "Ti" & "TD" signals are produced by the Engine control module and sent to the cluster. As first introduced on the E39, these signals were delivered to the cluster via hard wire. On models produced after 9/98 these signals are delivered by the CAN Bus.
The cluster processes the signals for the tachometer and fuel economy indicator displays. The Ti signal is used by the cluster for the SI indicator. The cluster also passes the TD signal out over the K Bus.
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Note. Diagram represents vehicles produced before 9/98.
Transmission One Way Data Signal- The AGS control module provides a one way data signal to the instrument cluster for signalling of the range selector position, driving program and for fault lamp activation. This signal is provided over the CAN Bus on vehicles produced after 9/98.
DIMMER SIGNAL - This is a pulse-width modulated signal from the LCM. It is used to control the intensity of the back lighting of the instruments and the LCDs when the lights are switched ON. This signal is also output over the K-Bus.
K-BUS Signalling - The Cluster receives signals for the Check Control Pictogram over the K-Bus.
Battery Voltage - Battery voltage is monitored by the cluster and a fault is stored if the voltage exceeds 16 volts.
Fuel Tank Level - Two lever action sensors are wired in parallel to the cluster. The two varying voltage signals are processed by the cluster for fuel gauge and low fuel warning display.
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Coolant Temperature - A NTC sensor is used to measure coolant temperature, the cluster uses this input for temperature gauge display. This is also a CAN bus signal on vehicles which have the CAN bus link to the cluster
Outside Temperature - A NTC sensor is used to measure the ambient temperature. The signal is processed by the cluster and passed out over the K Bus to modules requiring this input for processing.
The normal ignition switch terminals ( KLR, KL15 & KL50 ) are input to the cluster. Various functions are dependent on ignition switch position.
Steering Column Switch - The turn signal stalk provides a momentary ground signal that is used to call up BC functions.
Brake Pad wear Sensor - The pad sensor inputs are used to illuminate the brake pad warning indicator.
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Instrument Panel Button - The reset button is used to reset the trip - odometer as in the past. It will also display the mileage, if pressed with the key switched OFF. This button is also used for the Base BC/instrument cluster test functions.
Inputs for Warning Lamps - Various switches are used to signal the cluster for warning and indicator lamp illumination. Many of these inputs are provided over the CAN or K-bus.
Speed Signal "A" - The vehicle speed signal is available as an output for control modules that require precise vehicle speed information.
K-Bus Interface - The K Bus is used to transfer data between the cluster and other modules on the link. The diagnostic interface also passes over the K Bus for troubleshooting with the DIS.
Low Fuel - Based on the processing for the low fuel indicator lamp, this output is also sent to the Engine control module. The signal is stored along with a mis-fire detection fault for troubleshooting purposes.
Gong Output - T3, The T3 tone is used for check control warnings.
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Scheme 207
The specific information stored redundantly includes
- Vehicle ID number.
- Total mileage.
- Service Interval data.
The data is stored in the cluster and in the Light Check Module (LCM). The storage of this data follows the redundant storage of the IKE. It prevents the loss of total mileage or SI data in the event of a cluster processor failure.
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The data is compared each time KL 15 is switched ON. If the data does not match, the manipulation DOT in the mileage display is illuminated.
Because of this redundant storage feature, the following points must be noted
- If the vehicle ID number is not the same in both modules, the manipulation DOT is illuminated and no data transfer takes place. All functions of both modules will continue to operate.
- Data will only be accepted by the cluster from the LCM if the ID numbers match and the cluster mileage is zero.
- The vehicle ID number is input into the cluster through coding and will only be accepted when the cluster is at zero mileage.
- The LCM stored mileage can only be overwritten with a higher mileage and is updated every 60 miles.
- If the mileage differs by more than 120, and the ID numbers are the same, the cluster will continue recording the mileage and set a fault for data transfer.
- If the K Bus link to the LCM fails, the cluster will continue to record mileage and store a fault for the data link.
These conditions will only allow new components to be installed for replacement purposes. However, a used component can be installed for testing purposes. If a cluster from another vehicle is used for testing purposes, road testing of the vehicle should be avoided, because the cluster will accumulate mileage.