Displaying outside temperature, function - GF54.30-P-3019R

MODEL 230 

Networking 

Function requirements: 

The outside temperature indicator in the right multifunction display (A1p15)  uses the following data to display the temperature:

• The outside temperature reading
• The vehicle speed signal
• The coolant temperature
• The engine running time

Displaying outside temperature 

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

The fact that the outside temperature indicator in the right multifunction display (A1p15) 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 for max. 60 minutes.
  • 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 outside temperature rises above  the stored value, the current measured outside temperature is displayed after the following delay periods : 

• 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 previous engine running time was 5 minutes. The delay is thus 6 x 5 minutes. The current temperature is therefore 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 therefore 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 between 20 km/h  and 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.

Display range 

The display range is -40°C to +85°C or -40°F to +185°F.  The resolution is 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 of the left multifunction display (A1p13) to change the right multifunction display (A1p15).

Reading in the necessary data: 

• 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 of the outside temperature indicator temperature sensor (B14) is registered by the driver-side SAM control module  (N10/10).
  • The driver-side SAM control module (N10/10) converts the resistance value of the outside temperature indicator temperature sensor (B14) into a temperature value. 
  • The driver-side SAM control module (N10/10) relays this temperature value onto the interior compartment CAN.
• Vehicle speed signal 
  • The four RPM signals from the left front (L6/1), right front (L6/2), left rear (L6/3) and right rear (L6/4) wheel speed sensors are registered by the SBC control module (A7/3n1).
  • The SBC control module (A7/3n1)  relays the four wheel speed signals onto the engine compartment CAN via the ESP, SPS and BAS control module (N47-5). 
  • The instrument cluster (A1) uses these to calculate the vehicle speed. (See also the document entitled "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.)
  • The resistance of the coolant temperature sensor (B11/4) is registered by the ME-SFI control module (N3/10). 
  • The ME-SFI control module (N3/10) converts the resistance values of the coolant temperature sensor (B11/4) into a temperature value. 
  • The ME-SFI control module (N3/10) relays this temperature value onto the engine compartment CAN.
• Engine running time 
  • The engine running time is calculated internally in the instrument cluster (A1) by the integrated timer (z).
  • The instrument cluster (A1) 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 in continuity in the circuit. If the display indicates the maximum temperature of 85°C or 185°F, although the actual temperature is obviously lower, this could indicate a short circuit in either the sensor or the cable.

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