Displaying Outside Temperature

Networking:

The outside temperature indicator (A1p4) takes into account the following data for the display of the temperature value:
- the outside temperature value,
- the vehicle speed signal,
- the coolant temperature value,
- the engine running time

Displaying outside temperature
The instrument cluster (A1) processes this data and actuates the display accordingly.
The dependency of the outside temperature display (A1p4) on vehicle speed, the engine running time and coolant temperature, prevents a too high a temperature, which can for example be caused by heat radiation of the engine being displayed when the vehicle is stationary or driving slowly. The display behaves differently depending on the engine coolant temperature and engine running time:

- Coolant temperature below 60 °C
- When the instrument cluster (A1) is activated the current outside temperature value is always displayed.

- Coolant temperature the same as or above 60 °C
- When the ignition is switched off the temperature value last measured is stored and displayed.
- When the instrument cluster (A1) is activated the stored temperature value is displayed.

If the measured outside temperature drops below the stored value, the current measured temperature is displayed after 8 seconds.

If the outside temperature rises above the stored value, the current measured outside temperature is displayed after the following delays:

- When the engine is not running the current outside temperature is only displayed after 6 times the engine running time. The previous engine running time is taken as a basis for this.
Example:
The preceding engine running time was 5 minutes. The delay is then 6 x 5 minutes. So the current temperature is not displayed until after 30 minutes.
If the engine running time was more than 10 minutes, a maximum of 10 minutes is taken into account for the calculation of the delay. The maximum delay is therefore 60 minutes.

- When driving the delays depend on the vehicle speed:
- At vehicle speeds above 45 km/h rising outside temperatures are displayed after a delay of 1.5 minutes.
- At speeds of 20 km/h to 45 km/h rising outside temperatures are displayed after a delay of 3 minutes.
- If the speed drops below 20 km/h (starting from higher values), the display is only changed if the measured value drops.

Display range
The display range is -38 °C to + 58 °C or 36 °F to + 136 °F. The resolution is 0.5 °C or 1 °F.

Switching over from degrees Celsius to degrees Fahrenheit
The switchover from degrees Celsius to degrees Fahrenheit takes place via the "settings" function of the multifunction display (A1p13).

Reading in the data required:

- Outside temperature
- The ambient temperature display temperature sensor (B14) changes its resistance value according to the outside temperature. (This sensor is an NTC resistor, i.e. the resistance decreases as the temperature rises.)
- The resistance of the ambient temperature display temperature sensor (B14) is read in by the left front SAM control module (N10/6).
- The left front SAM control module (N10/6) converts the resistance value of the ambient temperature display temperature sensor (B14) into a temperature value.
- This temperature value is placed on the CAN interior by the left front SAM control module (N10/6).

- Vehicle speed signal
- The four wheel speed signals (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. (Also refer to document "Displaying vehicle speed, function".) Displaying Vehicle Speed

- Coolant temperature value
- The coolant temperature sensor (B11/4) changes its resistance according to the coolant temperature. (The sensor is an NTC resistor, i.e. the resistance decreases as the temperature rises.)
- 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 placed on the CAN engine compartment by the injection system control module (N3).

- Engine running time
The engine running time is determined internally by the integrated time generator (z) in the instrument cluster (A1).

The instrument cluster (A1) prepares this data and actuates the display accordingly.

Notes on diagnosis
If the display indicates the lower temperature value -38 °C or 36 °F when the outside temperature is obviously higher outside, there may be a broken sensor or a cable open-circuit. If the display indicates the highest temperature value 58 °C or 136 °F when the outside temperature is obviously lower, there may be a short-circuit in the sensor or cable.