Instrument Cluster (Standard Version)
Instrument Cluster (Redesign Standard Version):
This section applies to the Instrument cluster without check-control as of September 1990.
General:
The instrument cluster "Instrument Cluster Redesign Standard Version" is a further development (=Redesign) of the instrument cluster standard version installed up to September 1990.
Important modifications compared to old version:
- LCD module for odometer displays (6)
- LCD module for gear indicator with automatic transmission (7)
- Control unit has diagnostic capabilities
- Integrated test facilities
Analog Instruments
Fuel gauge (1): The immersion tube sending unit in the fuel tank indicates the amount of fuel in the tank. An indicator lamp in the fuel gauge lights when the fuel level drops below 8 litre. The tank indicator is set to zero when the reserve lamp lights.
This indicator lamp is damped "electronically", i.e. flicker of the lamp caused by movements of the fuel is suppressed.
Speedometer (2): The signals from the rear axle Reed contact (tachogenerator) are processed in the instrument cluster.
Tachometer (3): The TD-signal (engine speed signal) is processed by the OME or DDE control unit.
Temperature gauge (4): This gauge indicates the coolant temperature.
KVA Indicator (fuel consumption indicator) (9): The ti-signal (injection signal) of the DME control unit or the tQ-signal of the DDE control unit and the vehicle speed signal are processed. The current fuel consumption is calculated from both values.
Button (5):
The trip odometer can be reset with the button (5). If the button is pressed when the ignition is switched off, the total distance covered and the trip odometer are displayed for approx. 5 seconds. The system test can also be started with this button.
LCD Module (6):
The total distance covered, the trip odometer and the service intervals are displayed in the LCD module (LCD Liquid Crystal Display). The LCD module is lit by two 1.2 W lamps.
The brightness of the module is controlled automatically. A photoelectric sensor (8) senses the brightness in the vehicle and adjusts the illumination of the LCD module accordingly.
The brightness of the LCD module can also be adjusted by means of the dimmer when the vehicle lights are switched on. The dimmer also acts on the lighting in the analog instruments.
The brightness value determined by the photoelectric sensor (8) can be used as an output signal by other control units.
Program and Gear Indicator (7):
A further LCD module with separate connector is installed in vehicles equipped with automatic transmission. The program and gear are displayed in this module.
A fault symbol is displayed if the EGS control unit detects a fault.
Acoustic Relay:
A sound-generating relay is installed in the instrument cluster. The relay can be activated by the electronic circuitry with alternating frequencies.
The relay is used as:
- Turn signal sound generator
- Light warning (e.g. ignition OFF and parking light ON)
- Belt warning (USA and KSA only)
Coding Plug:
The coding plug is plugged into the instrument cluster. It basically consists of a voltage-independent electronic memory. This memory contains all specific vehicle data which the instrument cluster requires to process and display signals.
The total mileage and the service interval data are also stored in the memory.
Coding Plug Code:
The code is printed on a label on the reverse side of the coding plug. The code is also indicated in the diagnostic program (*D* Special functions: Coding Data) and during the integrated test.
Integrated Test Facilities:
Important data and the system test can be read out or triggered without diagnosis.
Procedure:
- Switch off ignition.
- Press instrument cluster button and hold depressed.
- Switch ignition switch to position R (position 1).
- Release instrument cluster button when the first output appears in the field for the mileage (total distance covered) in the LCD module.
Displays:
- 1: Internal number for monitoring purposes
- 2: Code number of coding plug
- 3: k-number (factor) for speedometer
- 4: Chassis number (last 7 digits)
- 5: Software version
- 6: Revision index
The corresponding numbering appears in the trip odometer field.
If the coding plug is a replacement plug, the red replacement marking lights during the display (red LED).
A system test is triggered on completion of these outputs.
System Test:
- All segments and the lighting of the LCD module are switched on. Also the red LED for replacement identification!
- The pointers of the speedometer, tachometer, fuel gauge, temperature gauge and KVA move, within 5 seconds, from the zero position to the end position and back.
- The warning lamps for brakes, tank reserve and belt (belt only in US, KSA version) are switched on.
The internal test procedure is terminated on completion of the system test. It can, however, be interrupted at any time by switching on the ignition (ignition switch in position 2).
Position of Indicator Lamps:
Indicator Lamps:
Number Indicator lamp Source
1 Left turn signal Relay
indicator
2 High beam Light switch
3 Right turn signal Relay
indicator
4 Trailer turn signal Relay
indicator
5 ASC (provisions) (ASC control unit)
6 Fog light Fog light switch
7 Rear fog light Fog light switch
8 Not used
9 Not used
10 Fuel filter (diesel only) Sensor on filter
11 DDE diagnosis (diesel only) DDE control unit
12 Preheating (diesel only) Preheating control unit
13 Start enable (diesel only) Preheating control unit
14 Battery charge indicator Alternator
15 Oil pressure Pressure switch
16 ABS indicator ABS control unit
17 Airbag Airbag control unit
18 Brake fluid Brake fluid level switch
19 Brake pad wear Brake pad contact
20 Hand brake Hand brake switch
21 Seat belt (USA and gulf Belt relay
States only)
22 self-leveling control
(provisions)
23 EDC (provisions)
24 Tank reserve Immersion tube sending unit with
electronic damping in instrument cluster
25 Over temperature
(not included at present)
Lamp Self-Test:
The lamps for oil pressure (15) and battery charge indicator (14) light when the ignition is switched on. They go out when the engine starts.
The lamps brake pad wear (19), tanks reserve (24), hand brake (20) and brake fluid (18) light for approx. 3 seconds and the lamps for airbag (17) and DDE (11) for approx. 6 seconds after the ignition has been switched on.
In diesel models, the preheating lamp (12) also lights when the ignition is switched on. After preheating, the start lamp (13) lights. If the vehicle is then not started, the start lamp also goes out after a short period of time. The preheating lamp lights up again when the ignition is switched on.
Depending on the ABS system installed in the vehicle, the indicator lamp for ABS (15) lights either continuously until the engine starts or for approx. 2 seconds after the ignition has been switched on.