General
The instrument cluster consists of 7 modules (4 modules with pointers and 3 modules with displays and controls) as well as a control unit containing the electronics controlling the modules. This control unit is connected to the vehicle wiring harness and contains the three bus interfaces (diagnosis bus, K-bus, CAN-bus), via which communication (serial data link) to the other control units is established as is communication with the connection to the sensors.
The instruments are divided into the modules for:
Replacement of control unit for instrument modules
The four cases described in the following show under which circumstances which steps must be taken to ensure correct replacement of the instrument cluster electronics.
Case 1: The control unit for the instrument modules is defective and the light check module control unit (LCM) is OK.
Measures |
Result |
Remarks |
---|---|---|
Replace control unit for instrument modules (new part) |
The manipulation point is set with the ignition switched on. |
The manipulation point is set since the vehicle identification number in the light check module differs from the vehicle identification number in the control unit for the instrument modules. |
Recode control unit for instrument modules |
|
Code control unit for instrument modules in accordance with the central coding code |
Code vehicle identification number in the control unit for the instrument modules |
|
Total distance recording (trip recorder only) will not take place in either the control unit for the instrument modules or the LCM if the vehicle identification number has not been coded in the control unit for the instrument modules. |
Switch off ignition and switch on again |
The manipulation point goes out, the control unit for the instrument modules adopts the total odometer reading (mileage) and the SIA data from the LCM. |
Data exchange between the control unit for the instrument modules and the LCM control unit for common data storage (SIA data, total odometer reading, vehicle identification number etc.) is now OK again. |
Case 2: The control unit for the instrument modules is OK and the light check module control unit (LCM) is defective.
Measures |
Result |
Remarks |
---|---|---|
Replace LCM (new part) |
The manipulation point is set with the ignition switched on. |
The manipulation point is set since the vehicle identification number in the light check module differs from the vehicle identification number in the control unit for the instrument modules. |
Recode LCM |
|
Code LCM with the central coding code |
Code vehicle identification number in the LCM |
|
As long as the vehicle identification number is not coded in the LCM, the total odometer reading will not be recorded in the LCM. |
Switch off ignition and switch on again |
The manipulation point goes out, the LCM adopts the total odometer reading (mileage) and the SIA data from the control unit for the instrument modules. |
Data exchange between the control unit for the instrument modules and the LCM control unit for common data storage (SIA data, total odometer reading, vehicle identification number etc.) is now OK again. |
Case 3: The control unit for the instrument modules and the light check module control unit (LCM) must be replaced.
Only replace both control units at the same time if this is unavoidable (stored total odometer reading is irretrievably lost).
Measures |
Result |
Remarks |
---|---|---|
Replace control unit for the instrument modules and LCM with battery disconnected (new parts) |
The manipulation point is set with the ignition switched on and the total odometer reading (mileage) is set to zero. |
The previous total odometer reading (mileage) is irretrievably lost. |
Code control unit for the instrument modules and LCM |
|
Code control unit for instrument modules and LCM in accordance with the central coding code |
Code vehicle identification number in the control unit for the instrument modules and in the LCM |
|
As long as the vehicle identification number is not coded, the total odometer reading (mileage) is recorded in the control unit for the instrument modules and in the LCM. |
Switch off ignition and switch on again |
The manipulation point goes out, the LCM adopts the total odometer reading (mileage) from the control unit for the instrument modules as well as the SIA data. |
The data exchange between the control unit for the instrument modules and the LCM for mutual data storage (SIA data, total odometer reading, vehicle identification number etc.) is now OK. again. |
Case 4: As a check, replace the control unit for the instrument modules or the light check module control unit (LCM).
Note
Although exchanging one of the two control units is possible in principle, it should be avoided wherever possible.
Measures |
Result |
Remarks |
---|---|---|
As a check, a control unit for the instrument modules or LCM control unit from another vehicle is installed. |
With the ignition switched on, the manipulation point is set and the control unit for the instrument modules continues to the total distance recording (mileage). |
As long as the vehicle identification number is different, the total odometer reading (mileage) is recorded only in the control unit for the instrument modules. There is no total odometer reading harmonization with the light check module (LCM). |
Test functions
System test (test No. 2): The system test serves the purpose of testing the display modules together with their elements which can be controlled from the control unit for the instrument modules.
These elements are:
Selecting test functions:
All test functions, apart from test numbers one and two, are interlocked and must be released by means of test function number nineteen.
Procedure: Press and hold (approx. 5 s) the trip recorder reset button with terminal R "ON" until "__tESt__1._" appears in the instrument cluster display. The corresponding test (system test corresponds to test 2 "__tESt__2._") can be selected by pressing/releasing the button again within 1 second. The first subfunction of the test selected then appears after approx. 1 second. The subfunction (the system test has no further subfunction) of the corresponding test can be selected by pressing the button again. Since there are no further subfunctions associated with test 2 (system test), the system test is triggered after the "__tESt__2.0" display appears and the trip recorder button is pressed. If the test is a locked test (test 3 to 21) the lock is released by pressing the trip recorder button when "_L_oFF" appears in the display. The display then jumps to test 0 so that the corresponding test can be selected by briefly pressing the button.
Test No. |
Function |
---|---|
1 |
Identification of the control unit for the instrument modules |
2 |
System test |
3 |
SIA data |
4 |
Current consumption values in l/100 km and l/h |
5 |
free |
6 |
Fuel tank content values |
7 |
Coolant temperature, outside temperature, current engine speed, current road speed |
8 |
ADC values (system voltage, voltage at left and right lever sensor, voltage at photo transistor and BVA, voltage at coolant and outside temperature sensor) |
9 |
System voltage terminal 30 in volts |
10 |
Read out country-specific code |
11 |
Read out units (AM/PM or mm.dd/dd.mm) etc. |
12 |
not used |
13 |
Triggering acoustic signals |
14 |
Read out of error bytes (self-diagnosis) |
15 |
Display of I/O port statuses |
16 |
Dimming value |
17 |
Internal clock |
18 |
free |
19 |
Locking and Unlocking Test Functions |
20 |
free |
21 |
Reset instrument cluster (software reset) |
0 |
End of test, the test mode can be quit with this function. |
The speed display module is equipped with different displays/indicators depending on the country-specific variant.
It also contains the warning lamps for the traction control system (ASC/DSC, yellow), the electronic engine management (EML) and a display (LCD) which shows the total distance recording, trip recording and service interval indicator. The service interval indicator corresponds to the SIA4 with consumption-dependent indication of the distance-dependent service, i.e. the remaining distance to inspection is indicated and, if coded, the time-dependent service where the date the service is due is indicated. The distance points for the speed display (speedometer) comes from the ASC/DSC control unit and is the conditioned signal from the rear left wheel speed sensor.
The module for the engine speed display (tachometer) also contains the warning lamps for battery charge indicator, convertible soft top, tyre failure warning system (RFC, DWS), antilock brake system (ABS, yellow), general brake warning, check engine and oil pressure/oil level warning (red/yellow). In addition, an analog clock that can be set forward and backward is also integrated in the module.
The engine speed display is controlled by the control unit for the instrument modules and the engine speed information is made available to the other control units via the K-bus. The engine speed information 0 [rpm] is output when the ignition is switched off.
The fuel gauge module also contains the warning lamp for fuel reserve indication.
The fuel tank content is measured by means of a lever-type sensor that is connected to the control unit for the instrument modules. The lever-type sensor is connected by a separate ground (analog ground) and a sensor line (analog positive) to the control unit. There is no reserve contact in the level sensor to activate the fuel reserve warning lamp. The "fuel reserve" signal is output as information for engine management. The fuel reserve warning lamp is switched as a function of the tank contents by comparison with a reserve threshold value. Determination of the fuel level is adapted to the shape of the fuel tank by means of the coding data and the resistance characteristics of the fuel level sensor.
The module for the coolant temperature gauge also contains the warning lamp for coolant overheating.
The coolant temperature is measured in the engine control unit and is read by the control unit for the instrument modules via the CAN-bus. The control unit determines the current coolant temperature from the CAN-bus information. The "coolant temperature" information is then made available to the other systems via the K-bus.
The control unit for the instrument modules also determines the coolant temperature with its own sensor (NTC). This temperature is indicated in the module for the coolant temperature gauge during the CAN-bus initialization phase.
Since, after shut-down, the engine still heats the coolant for a certain period of time, an increase in the gauge temperature when the engine is stationary is prevented by a "post-heating filter" in the software of the control unit for the instrument modules. When the engine is restarted, this function detects a higher temperature than at "engine off" and indicates this "engine off" value. The current temperature is then indicated after approx. 20 seconds with the engine running.
At "ignition on", the control unit for the instrument modules switches on the coolant temperature warning lamp for 2 seconds (predrive check). It is then controlled by the engine control unit via the CAN-bus. If the coolant temperature warning lamp is switched on by the engine control unit, this CAN message is made available on the K-bus to other control units.
The control unit for the instrument modules receives the value via the CAN-bus and correspondingly controls the coolant temperature gauge. On reaching the maximum value, the pointer is moved to the middle of the red warning zone.
The service interval display (SIA) shows the driver and the workshop when an engine oil service, distance-dependent service or a time-dependent service is due. The service intervals of the vehicle are not rigidly related to the kilometres covered but rather they depend on the consumption. The current service interval status is displayed from "Terminal 15 ON" for 10 seconds after a minimum engine speed of 400 rpm is reached.
The service interval display (SIA) data is also stored in the light check module (LCM).
The service interval display (SIA) is reset by pulses of defined length at the service interval reset input. Each reset procedure can be carried out individually (service interval display [SIA] reset). The oil service, time-dependent service and/or distance-dependent service can be reset.
The display indicating the total driven distance is an integral part of the LC display in the speed display (speedometer) module. The current mileage is indicated on the display from terminal R "ON". With terminal R "OFF", pressing and releasing the trip recorder reset button displays the mileage for approx. 25 seconds. The unit of distance (km/miles) dependent on the coded country-specific version is displayed between the total distance recorder and the trip recorder. The total distance is placed on the body bus as a telegram (K-bus).
The total distance is stored in the control unit for the instrument modules and in the light check module (LCM).
The display indicating the trip distance is an integral part of the LC display in the speed display (speedometer) module. The current trip recorder reading is shown on the display from terminal R "ON". At terminal R "OFF", pressing and releasing the instrument cluster button displays the mileage for approx. 25 seconds. The unit of distance (km/miles) dependent on the coded country-specific version is displayed between the total distance recorder and the trip recorder.
The control unit that contains the electronics for controlling the modules determines the current outside temperature from on the outside temperature sensor (NTC resistor). The outside temperature sensor is connected by its own ground (analog ground) and a sensor line (analog positive) to the control unit that contains the electronics for controlling the modules.
The "outside temperature" information is transferred by the instrument cluster to the bus and indicated by the multi-information radio (MIR). In ignition lock position "0", the outside temperature sensor is read by the control unit for the instrument modules at time intervals which are within the minute range. For this purpose, the instrument control unit is briefly activated, it provides the "outside temperature" information and then switches off again (sleep mode).
Instrument dimming and illumination of the LC display are controlled in different ways. The light module section in the light check module (LCM) uses the pulse-width modulated signal (58g) for the purpose of dimming the instruments. With the lights switched off, the brightness information from the phototransistor integrated in the speedometer module is used to control the lighting of the LC display, thus adapting the lighting of the LC display to ambient light conditions. With the lights switched on, the illumination intensity of the LC display can be additionally varied within a limited range by means of the dimmer. However, the ambient light information acquired via the phototransistor has priority in controlling the lighting intensity of LC display.
Warning lamps |
Required signal |
---|---|
General brake warning lamp |
Lit red: Parking brake applied with ignition switched on (ground from parking brake switch). Brake fluid level message via bus from light check module or malfunction message on CAN-bus or "electronic brake power distribution (EBV)" failed message from ASC control unit. |
|
Lit yellow: Malfunction message via the CAN-bus "brake assistant (HBA)" from ASC control unit. |
Seat belt indicator lamp |
K-bus message from light check module (dependent on coding data) |
Fuel reserve lamp |
Resistance value of fuel tank lever-type sensors (analog input) |
Turn signal indicator lamps |
Bus message from light check module |
Rear fog light indicator lamp |
Bus message from light check module |
High beam indicator lamp |
Bus message from light check module |
Oil indicator lamp |
Lit red: Oil pressure warning through oil pressure switch ground |
|
Lit yellow: Oil level warning bus message |
Coolant over-temperature (red) |
Bus message via CAN-bus from engine control unit |
Battery charge indicator lamp |
Compact alternator signal "no charge" |
ABS indicator lamp |
Signal from antilock brake system control unit |
Airbag indicator lamp |
Signal from airbag control unit |
Check engine (exhaust gas warning lamp) |
Bus message via CAN-bus from engine control unit |
ASC control |
Bus message via CAN-bus from chassis (wheel traction) control unit |
Tyre failure warning |
Bus message from tyre failure monitoring system |
EML indicator lamp (electronic engine management) |
Bus message via CAN-bus from engine control unit |
Brake pad wear warning lamp |
Signal loop via brake pad sensors |
Convertible soft top warning lamp |
Signal from convertible soft top module |
General: LEDs provide the background lighting of all warning lamp symbols. Two-coloured LEDs are used for symbols that can light up red or yellow.
General brake warning lamp: The warning lamp (red) can be switched on by the light check module (LCM) via the bus when the LCM detects that the brake fluid level is too low. The warning lamp (red) is also activated by the chassis control unit (ASC) if a malfunction in the electronic brake power distribution (EBV) is detected by the ASC or no ASC message is sent on the CAN-bus from the ASC control unit to the control unit for the instrument modules. The warning lamp is also activated after ignition ON with parking brake applied or for checking the function (predrive check). As part of the predrive check, the warning lamp lights up red and yellow for 1 second if the function for the brake assistant (HBA) is coded otherwise the warning lamp will light up only red for 2 seconds. The warning lamp will light only red if the parking brake is applied.
The warning lamp will light only yellow if no warning for red is applicable. The warning lamp (yellow) is activated by the chassis control unit (ASC) via the CAN-bus if the ASC detects a malfunction in the brake assistant (HBA).
Seat belt indicator lamp: The seat belt indicator lamp is activated dependent on the coding data. For vehicles without a seat belt buckle contact, it is switched on for approx. 6 seconds after terminal 15 "ON".
Bus telegram from light check module (LCM) activated until the seat belt contact is opened (seat belt buckle latched).
Fuel reserve lamp: The fuel reserve warning lamp is not switched by a reserve contact in the level sensor. It is switched as a function of the tank contents by comparison with a reserve threshold value.
The "fuel reserve" signal is output as information for engine management. As a function check, the fuel reserve warning lamp is switched on for 2 seconds when terminal 15 is switched on (predrive check).
Turn signal indicator lamps: The turn signal indicator lamps are switched by means of a corresponding bus telegram from the light check module (LCM) to the control unit for the instrument modules.
Rear fog light indicator lamp: The rear fog light indicator lamp is switched by means of a corresponding I-bus telegram from the light check module (LCM) to the control unit for the instrument modules.
High beam indicator lamp: The high beam indicator lamp is switched by means of a corresponding I-bus telegram from the light check module (LCM) to the control unit for the instrument modules.
Oil pressure indicator lamp: The warning lamp (red) is switched by the oil pressure switch.
The warning lamp (yellow) is switched by means of a corresponding K-bus telegram from the light check module (LCM) to the control unit for the instrument modules. The engine control unit evaluates the signal from the oil level sensor in the engine, it sends a CAN message to the control unit for the instrument modules that converts the CAN-message and sends it in the form of a K-bus message to the light check module. The light check module modifies the information according to the coding data and sends a K-bus telegram to the control unit for the instrument modules which in turn controls the oil level warning thus prioritizing the oil pressure warning.
The oil indicator lamp lights yellow under following conditions:
Coolant temperature warning lamp: At "ignition on", the control unit for the instrument modules switches on the coolant temperature warning lamp for 2 seconds (predrive check). It is then controlled by the engine control unit via the CAN-bus. If the coolant temperature warning lamp is switched on by the engine control unit, this CAN message is made available on the connected bus systems to other control units.
Battery charge indicator lamp: The warning light is switched by the compact alternator with a signal line ("no charge") to the control unit for the instrument modules.
Antilock brake system indicator lamp: The warning lamp is switched by the ABS system. The warning light must also be activated in the event of an open circuit in the signal line. The signal line high (system voltage) warning lamp active, signal line low (ground) warning lamp off and signal line high (high-ohmic, interrupted) warning lamp active function handles a break in the signal line.
Airbag indicator lamp: The warning lamp is switched by a signal (ground) from the airbag control unit.
Check engine (exhaust gas warning lamp): The "check engine" warning lamp is switched by the engine control unit via the CAN-bus.
Warning light for automatic stability control (ASC): The ASC warning light is switched by the ASC system via the CAN bus. In order to check the function, after switching on the ignition, the warning light is switched on by the ASC system for a defined period of time (predrive check).
Warning light for tyre failure warning system (DWS / RFC): The tyre failure warning light is switched by the tyre failure warning system via a corresponding bus telegram to the control unit for the instrument modules.
To check its function, the warning light is switched on for 2 seconds (predrive check) if the system is coded in the coding data of the control unit for the instrument modules.
Warning light for electronic engine management (EML): The EML warning light is switched by the engine control unit via the CAN-bus. If no EML message is received on the CAN-bus from the engine control unit by the control unit for the instrument modules the warning light is switched on 1.5 seconds after the ignition is switched on (emergency mode value).
Brake pad wear warning (BBV): The brake pad wear warning light is located in the left-hand turn signal indicator module and is activated by the control unit for the instrument modules. The warning light is switched on for approx. 2 seconds after the ignition is switched on as a function check (predrive check).
The sensors consist of a conductor loop in each of the rear right and front left brake pads and are connected in series. In the case of a worn brake pad, the conductor loop is interrupted. This is detected by the control unit and consequently the warning light is activated. The indication is cancelled if the interruption is no longer detected for 30 seconds after the ignition is switched on and the engine is not running.
Convertible soft top warning light: The warning light for the convertible soft top is activated by the convertible top module (CVM) via a signal line. The warning light comes on when the convertible soft top is operated. The warning light will flash if the convertible soft top is not locked in its end position.
The acoustic generator for the light warning and for switching the direction indicators is integrated in the module for the speed display (speedometer). The light warning will sound for 8 cycles (1 cycle = 500 ms ON / 500 ms OFF) if the ignition lock is in position "0", the driver's door is opened for the first time and the instrument lighting is switched on. The information required for triggering the light warning is read via the K-bus and linked and controlled by the control unit for the instrument modules.
The "ignition key warning" function is included in the coding data and is only executed by the control unit for the instrument modules if it is coded accordingly (normally in USA version only). The light check module triggers the acoustic warning via a K-bus telegram. Consequently the control unit for the instrument modules activates gong tone 3 (T3).
The ignition key warning is triggered for max. 60 seconds when the ignition is switched off and the driver's door is open. The warning is cancelled immediately if a corresponding K-bus telegram is received by the control unit for the instrument modules from the light check module.
The acoustic generator for switching the direction indicators and the light warning are integrated in the module for the speed display (speedometer). The control unit for the instrument modules activates the acoustic relay in synch with the left and right direction indicators as well as the turn signal indicator lights. The light check module sends the "direction indicator switched on" information via the K-bus thereby also controlling the synchronization. If detected, a defect in a direction indicator lamp is indicated to the control unit for the instrument modules in the K-bus telegram. The two indicator lamps are then driven at double the clock frequency.
The control unit for the instrument modules activates tone 3 (T3) in the gong. Depending on the coding data and the corresponding K-bus information, an acoustic warning is triggered for the seat belt warning, ignition key warning, parking brake warning, tyre failure warning and speed warning. Depending on the type of warning, tone 3 (T3) is sounded repeatedly or once only.
Acoustic seat belt warning: An acoustic seat belt warning is only possible in connection with a driver's seat belt buckle contact and corresponding coding. The light check module triggers and terminates the warning via the K-bus. When the seat belt contact is open, the control unit for the instrument modules activates gong tone 3 (T3) intermittently for max. 6 seconds after the ignition is switched on. The gong is switched off if the seat belt is buckled before this period of time elapses.
Acoustic ignition key warning: Corresponding to the coded data the ignition key warning is triggered for max. 60 seconds when the ignition is turned off and the driver's door is open. The warning is cancelled immediately if a corresponding K-bus telegram is received by the control unit for the instrument modules from the light check module.
Acoustic speed warning: Corresponding to the coded data, a speed warning is triggered by the control unit for the instrument modules. A short tone 3 (T3) sounds at the gong if the speed threshold is exceeded. If the speed drops below this threshold by more than 5 km/h the tone will be triggered again when the threshold is exceeded.
Parking brake warning: Depending on the coded data, a parking brake warning is triggered at the gong as soon as the parking brake is applied and a road speed of more than 3 km/h is detected. The intermittent tone sounds for as long as the warning status applies, however, for maximum 20 seconds.
Acoustic tyre failure warning: The tyre failure warning light signal is switched via the K-bus from the tyre failure warning system to the control unit for the instrument modules. If the acoustic tyre failure warning is coded, an acoustic warning is also triggered when the ignition is turned on.
Summary of gong variants
Warning |
Type of gong |
Condition |
---|---|---|
Seat belt warning via seat belt buckle contact |
Intermittent gong max. 6 seconds long |
Ignition ON and seat belt not buckled (K-bus information) |
Ignition key warning |
Intermittent gong max. 60 seconds long |
Ignition OFF, driver's door open and ignition key inserted (K-bus information) |
Speed warning |
Single gong tone 3 (T3) |
Ignition ON, vehicle in motion and exceeding threshold |
Parking brake warning |
Intermittent gong max. 20 seconds long |
Ignition ON, vehicle driving faster than 3 km/h and parking brake is applied |
Tyre failure |
Single gong tone 3 (T3) |
Ignition ON, tyre failure detected (K-bus information) |