Displaying Outside Temperature
Networking:
The outside temperature indicator (A1p4) takes the following data into account when displaying the temperature value:
- the outside temperature value,
- the vehicle speed signal,
- the coolant temperature value,
- the engine operating time
Displaying outside temperature
The instrument cluster (A1) processes the data and actuates the display accordingly.
Due to the dependence of the outside temperature indicator (A1p4) on the speed, engine operating time and coolant temperature, a temperature which is too high, as can be caused by heat radiated from the engine for example, is prevented from being displayed when the vehicle is stationary or when driving slowly. The display behaves differently depending on the coolant temperature and engine operating time:
- Coolant temperature below 60 °C
- The current outside temperature value is always displayed when the instrument cluster (A1) is activated.
- Coolant temperature equal to or above 60 °C
- The last measured temperature value is stored and displayed when the ignition is switched off.
- The stored temperature value is displayed when the instrument cluster (A1) is activated.
If the outside temperature measured drops below the stored value, the current temperature measured is displayed after 8 seconds.
If the outside temperature measured rises above the stored value, the current temperature measured is displayed after the following time delays:
- When the engine is not running the current outside temperature is only displayed after 6 times the engine operating time. The previous engine operating time is taken as a basis.
Example:
The previous engine operating time was 5 minutes. The time delay is then 6x5 minutes. The current temperature is therefore only displayed after 30 minutes.
If the engine operating time was more than 10 minutes, a maximum of 10 minutes is taken into account when calculating the time delay. The maximum delay is therefore 60 minutes.
- When driving the time delays depend on the vehicle speed:
- At speeds above 45 km/h, rising outside temperatures are displayed after a time delay of 1.5 minutes.
- At speeds between 20 km/h and 45 km/h, rising outside temperatures are displayed after a time delay of 3 minutes.
- When dropping below a speed of 20 km/h (coming from higher values), the display only changes when the measured value drops.
Display range
The display range is -38 °C to + 58 °C or
Switching over from degrees centigrade to degrees Fahrenheit
Switching over from degrees centigrade to degrees Fahrenheit takes place via the "settings" function of the multifunction display (A1p13).
Reading in the required data:
- Outside temperature
- The outside temperature indicator (A1p4) changes its resistance value corresponding to outside temperature. (The sensor is an NTC resistance, i.e. the resistance decreases as temperature increases).
- The resistance of the outside temperature indicator (A1p4) sensor is read in directly by the instrument cluster (A1).
- Vehicle speed signal
- The four wheel speed sensors (L6/1, L6/2, L6/3, L6/4) are read in by the traction Systems control module (N47).
- The traction systems control module (N47) places the four wheel speed signals on the CAN/engine compartment.
- The instrument cluster (A1) determines the vehicle speed from this. (See also "Displaying vehicle speed, function" document.) Displaying Vehicle Speed
- Coolant temperature value
- The coolant temperature sensor (B11/4) changes its resistance depending on coolant temperature. (The sensor is an NTC resistance, i.e. the resistance decreases as temperature increases).
- The resistance of the coolant temperature sensor (B11/4) is read in by the injection system control module (N3).
- The injection system control module (N3) converts the resistance values of the coolant temperature sensor (B11/4) into a temperature value.
- This temperature value is sent to the CAN/engine compartment by the injection system control module (N3).
- Engine operating time
The engine operating time is determined inside the instrument cluster (A1) with the integrated time generator (z).
The instrument cluster (A1) processes this data and actuates the display accordingly.
Notes on diagnosis
If the display shows the lower temperature value -38 ° C or 36 ° F when the outside temperature is obviously higher, there may be a broken sensor or a cable open-circuit. If the display shows the highest temperature value 58 ° C or 136° F when the outside temperature is obviously lower, there may a short-circuit in the sensor or cable.