Displaying outside temperature, function - GF54.30-P-3019S
Model 215, 220
Networking of components Shown on Model 220
Basic requirements
Basic requirements for display of outside temperature:
- Outside temperature
- Vehicle speed signal
- Coolant temperature
- Engine running time
Displaying outside temperature
The instrument cluster (A1) processes these data as the basis for generating the display. The fact that the outside temperature indicator (A1p4) 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:
- When the instrument cluster (A1) is activated, the current outside temperature is always displayed.
Coolant temperature equal to or greater than 60 °C:
- When the ignition is switched off, the last measured temperature value is stored and displayed.
- When the instrument cluster (A1) is activated, the stored temperature is displayed.
If the measured outside temperature falls below the stored value, the current measured temperature is displayed after 8 seconds.
If the measured outside temperature rises above the stored value, the current measured temperature is displayed after the following delay periods:
- When the engine is switched off, the current outside temperature is displayed after six times the engine running time. This is based on the previous engine running time.
Example:
- Previous engine running time was 5 minutes; the delay time is 6 x 5 minutes. The current temperature is therefore displayed after a delay of 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 therefore 60 minutes.
When the vehicle is moving, the delay periods depend on the ground speed.
- At speeds in excess of 45 kph, increasing outside temperatures are displayed after a delay of 1 1/2 minutes.
- At speeds of 20 to 45 kph, increasing outside temperatures are displayed after a delay of 3 minutes.
- If the speed falls below 20 kph (from higher values), the display is only changed if the measured value falls.
Reading range:
The reading range is -38 to +58 degrees Celsius or -36 to +136 degrees Fahrenheit. Temperatures are graduated in steps of 0.5 degrees Celsius or 1 degree Fahrenheit.
Changing from degrees Celsius to degrees Fahrenheit
The driver can switch between degrees Celsius and degrees Fahrenheit using the "Settings" function on the multifunction display (A1p13).
Reading in required data for displaying outside temperature:
- The outside temperature display 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.)
- This resistance value from the outside temperature display temperature sensor (B14) is read in by the left front SAM control unit (N10/6).
- The left front SAM control unit (N10/6) converts the resistance value from the outside temperature display temperature sensor (B14) into a temperature value.
- This temperature value is sent by the left front SAM control unit (N10/6) to the interior compartment CAN.
Vehicle speed signal:
- The four wheel speed signals are read in by the wheel speed sensors of the traction systems control unit (N47).
- The traction systems control unit (N47) sends the four wheel speed signals to the engine compartment CAN.
- The instrument cluster (A1) uses the signals to determine the vehicle speed (see also the document "Displaying speed, function").
Coolant temperature:
- The coolant temperature sensor (B11/4) changes its resistance according to the coolant temperature. (The sensor is an NTC resistor, i.e. its resistance decreases as the temperature rises.)
Reading in coolant temperature:
- The resistance of the coolant temperature sensor (B11/4) is read in by the motor electronics control unit (N3/10) or by the CDI control unit (N3/9) and the resistance value from the coolant temperature sensor (B11/4) is converted into a temperature value.
- This temperature value is then sent to the engine compartment CAN.
Engine running time:
- The engine running time is determined internally in the instrument cluster (A1) using the integrated timer (z).
The instrument cluster (A1) processes this data and actuates the display accordingly.
Notes on diagnosis
If the display shows the lowest temperature value of -38 °Cor36°F when the outside temperature is obviously higher, the sensor may be faulty or there may be an open circuit.
If the highest temperature, 58 °C or 136 °F, appears on the display when the outside temperature is obviously lower, there may be a short circuit in the sensor or the wire.
| Instrument cluster (IC), location / task | GF54.30-P-3039S |