Instrument Cluster / Carrier: Description and Operation
Instrument Cluster:
Functional Description:
General:
The instrument cluster contains indicator/display instruments, indicator lamps and an LCD module (display unit).
Connection with EKM:
The EKM transfers a large number of data to the instrument cluster. These data are transferred via a data link, the instrument cluster data link (serial interface). This data link to the instrument cluster is independent of the I-bus (instrument bus). For description of the EKM, see Electronic Vehicle Module.
Engine Speed Measurement:
The tD signal (engine speed signal) for the tachometer is connected directly to the instrument cluster.
Scope of Functions The following functions are indicated:
Notes on Operation:
Measurement of tank contents: The tank contents are recorded and calculated by way of two lever-type sensors and the ti signals from the EKM. No reserve contact is provided for the fuel reserve lamp. On the basis of the content measurement/calculation, the lamp is switched on at a fuel reserve of approx. 10 l.
Vehicle speed: The rear axle reed contact (speed sensor) is connected to the EKM. The speed-A signal (output for other control units) is also connected to the EKM. Only the speed and distance are indicated in the instrument duster.
Total distance: The total distance is stored in the EKM and in the instrument cluster. When one unit is replaced, the value is adopted automatically .
Turn signal acoustic relay: An acoustic relay is installed in the instrument cluster which provides an acoustic signal when the turn signal indicator is switched on.
Internal and External Lamps:
Internal lamps: Internal lamps are switched on by the microprocessor of the instrument cluster. They can be checked by way of the *D* system test (special functions).
The internal lamps for fuel reserve, hand brake and brake warning light are switched on for 3 seconds after switching on the terminal 15.
External lamps: External lamps have no connection to the electronics of the instrument cluster. They are connected to ground or B+ via the instrument cluster and are switched on by means of a switch (e.g. fog light) a relay (turn signal indicator) or a control unit (e.g. airbag, EML, ABS, etc.).
System Test:
The system test makes it possible to activate all indicator instruments, internal lamps and the display unit (LCD display). Internal data are output via the display unit. If the instrument cluster and the EKM are replaced and record at the same time, the exchange point is activated during the entire test.
Start System Test in Vehicle:
- Switch off ignition (ignition in position 0)
- Press button for trip odometer reset and hold depressed
- Switch ignition from position 0 to position 1 (terminal P) or 2 (terminal 15).
- Start system test, the trip odometer reset button can be released.
End System Test :
Switch off ignition in vehicle
Test Procedure:
The pointers of the indicator instruments move from the zero position to full deflection and back.
The internal lamps are switched on.
The following appear in succession in the display unit:
If the instrument cluster and EKM are replaced, the manipulation point is switched on during the entire system test
Trip Odometer:
Two independent trip odometer readings can be stored in the instrument cluster. The display can be switched over between the two readings by turning the trip odometer reset button. The displayed value is cleared by pressing the button.
The digits I or II to the right next to the trip odometer display indicate which reading is displayed.
Coding Data:
All coding data as well as the stored values for:
- Total mileage
- Distance and time for service interval display
- Chassis number
are stored in the instrument cluster and in the EKM. If the instrument cluster is replaced, the data are immediately adopted from the EKM as soon as the terminal R is switched on. If a used unit is installed, e.g. from a different vehicle, this data exchange does not take place.
Identifier: Used/test phase:
Test phase means: The instrument cluster is not permanently assigned to the vehicle. If the unit is installed in another vehicle, it adopts the data (coding data, distance and SIA data) of the EKM.
Used means: The instrument cluster has been installed in the vehicle for at least 8 running hours (running hour = terminal R ON) and is therefore permanently assigned to the vehicle. If the unit is installed in another vehicle, data exchange will not take place. If a new EKM is installed, it will adopt the data (coding data), distance and SIA data) from the instrument cluster.