GF54.30-P-3019GZ Display Outside Temperature, Function

GF54.30-P-3019GZ Display Outside Temperature, Function

Component Identification:

Function requirements
The outside temperature indicator in the multifunction display uses the following data to display the temperature:
^ Outside temperature value
^ Vehicle speed signal
^ Coolant temperature
^ Engine running time

Displaying outside temperature
The instrument cluster conditions this data and actuates the display accordingly.

The fact that the outside temperature indicator in the multifunction display is dependent on the vehicle speed, the engine running time and the coolant temperature helps to prevent the display of too high a temperature when the vehicle is stationary or traveling slowly, such as might occur e.g. due to heat radiating from the engine.
The display behaves differently according to the coolant temperature and the engine running time. Coolant temperature below 60 °C:
^ The current outside temperature value is always displayed when the instrument cluster is activated.

Coolant temperature equal to or greater than 60 °C:
^ At "circuit 15C" the last measured temperature is stored and then displayed for a maximum of 60 minutes.
^ The stored temperature value is displayed when the instrument cluster is activated.

If the measured outside temperature falls below the stored value, the current measured temperature is displayed after 8 seconds. If the engine is off, the current outside temperature is displayed after six times the engine running time. This is based on the previous engine running time.

Example:
The preceding engine running time was 5 minutes. The delay period was then 6 times 5 minutes. The current temperature is thus only displayed after 30 minutes.
If the engine running time was more than 10 minutes, a maximum of 10 minutes is taken into account when calculating the delay time. The maximum delay is thus 60 minutes.

When the vehicle is moving, the delay periods depend on the vehicle speed. At speeds above 45 km/h rising outside temperatures are displayed after a delay period of 1.5 minutes.
At speeds of 20 km/h to 45 km/h rising outside temperatures are displayed after a delay period of 3 minutes. If the vehicle speed falls below 20 km/h (slowing from higher speeds), the display is only changed if the measured value falls.

Range
The display range is -40 °C to +85 °C or -40 °F to 185 °F. The temperature is displayed in increments of 0.5 °C or 1 °F.

Switching from degrees Celsius to degrees Fahrenheit
The driver can switch between degrees Celsius and degrees Fahrenheit using the "Settings" function in the multifunction display.

Data for outside temperature
The outside temperature indicator temperature sensor (B14) changes its resistance according to the outside temperature. The sensor is an NTC resistor, i.e. its resistance decreases as the temperature rises.
The resistance value from the outside temperature indicator temperature sensor is read in by the AAC [KLA] control and operating unit (N22).
The AAC [KLA] control and operating unit converts the resistance value from the outside temperature display temperature sensor into a temperature value and passes the temperature value onto the instrument cluster via the interior CAN.

Vehicle speed signal
The ABS, BAS and traction system hydraulic unit (A7/3) are integrated in the ESP control unit.

The following signals are read in by the ESP control unit
^ Left front rpm sensor
^ Right front rpm sensor
^ Left rear rpm sensor
^ Right rear rpm sensor

The ESP control unit places the four wheel speed signals on the engine compartment CAN.
The instrument cluster determines the vehicle speed from this.

Coolant temperature
The coolant temperature sensor changes its resistance according to the coolant temperature. (The sensor is an NTC resistor, i.e. its resistance decreases as the temperature rises.) The resistance from the coolant temperature sensor is read in via the ME-SFI [ME] control unit or the CDI control unit.

The ME-SFI [ME] control unit or CDI control unit converts the resistance values from the coolant temperature sensor into a temperature value
This temperature value is placed on the CAN engine compartment by the ME-SFI [ME] control unit or by the CDI control unit.

Engine running time
The engine running time is calculated internally in the instrument cluster using the integral timer.
The instrument cluster processes this data and actuates the display accordingly.

Notes on diagnosis
If the display indicates the minimum temperature of -40 °C or -40 °F although the actual temperature is obviously higher, this could indicate a defective sensor or an open wire in the circuit. If the display indicates the maximum temperature of 85 °C or 185 °F, although the actual temperature is obviously colder, this could indicate a short circuit in either sensor or wiring.

If the coolant temperature sensor is defective and no valid coolant water temperature is passed on from the CAN engine compartment, processing changes over into the range for coolant temperature of 60 °C.