Displaying outside temperature, function - GF54.30-P-3019PP
MODELS 203.0 /2 /7 up to 23.4.04
The outside temperature indicator (A1p4) takes into account the following data for displaying 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 drives the display accordingly. In addition the value is output on the Controller Area Network bus class C (engine compartment) (CAN-C).
Through the dependency of the outside temperature indicator (A1p4) on vehicle speed, engine running time and coolant temperature when the vehicle has stopped or is being driven slowly, too high a temperature, such as can be caused by heat radiation from the engine, is prevented from being displayed.
Depending on coolant temperature and engine running time the display behaves differently, with dropping temperatures always being displayed.
When the coolant temperature is 60 °C the current outside temperature value is always displayed when the instrument cluster (A1) is activated.
When the coolant temperature is ≥ 60 °C with "circuit 15 OFF" the temperature value last measured is stored and displayed.
The stored temperature is displayed when the instrument cluster (A1) is activated. If the outside temperature measured drops below the stored value, the temperature currently measured is displayed after t = 8 seconds.
If the outside temperature rises above the stored value when the engine is not running, the outside temperature measured is only shown on the multifunction display (A1p13) after 6-times the engine running time. This is based on the preceding engine running time.
Example: Delay period for outside temperature indicator
The preceding engine running time was t = 5 minutes. The delay period was then 6 x 5 minutes. The current temperature is therefore only displayed after t = 30 minutes. If the engine running time was more than t = 10 minutes, a maximum of t = 10 minutes is taken into account for calculating the delay period.
As a result the maximum delay is t = 60 minutes.
When the vehicle is moving, the delay periods depend on the ground speed.
- At speeds > 45 km/h rising outside temperatures are displayed after a delay period of t = 1.5 minutes.
- At speeds of 20 to 45 km/h rising outside temperature are displayed after a delay period of t = 3 minutes.
- With a reduction in speed < 20 km/h the display is only changed when the measured outside temperature value drops.
Range
The display range is -40 to +85 °C or -40 to +185 °F. The temperature is displayed in increments of 0.5 °C or 1 °F.
Changing over from degrees Celsius (°C) to degrees Fahrenheit (°F)
The changeover from degrees Celsius (°C) to degrees Fahrenheit (°F) take place via the "adjustments" function of the multifunction display (A1p13).
Reading in the required data for outside temperature:
- The outside temperature indicator temperature sensor (B14) changes its resistance according to the outside temperature. The sensor has an NTC resistance, i.e. the resistance reduces as temperature increases.
- The resistance of the outside temperature indicator temperature sensor (B14) is read by the front SAM control unit with fuse and relay module (N10/1).
- The front SAM control unit with fuse and relay module (N10/1) converts the resistance value of the outside temperature display temperature sensor (B14) into a temperature value.
- This temperature value is placed on the (N10/1) Controller Area Network bus class B (interior) (CAN-B) by the front SAM control unit with fuse and relay module.
Reading in the data for the vehicle speed signal:
- The left front rpm sensor (L6/1), right front rpm sensor (L6/2), left rear rpm sensor (L6/3) and right rear rpm sensor (L6/4) are read in by the ESP and BAS control unit (N47-5).
- The ESP and BAS control unit (N47-5) places the signals from the left front rpm sensor (L6/1), right front rpm sensor (L6/2), left rear rpm sensor (L6/3) and right rear rpm sensor (L6/4) on the CAN-C.
- The instrument cluster (A1) reads out this information from the CAN-C and determines the speed of the vehicle from it.
The engine running time is determined internally in the instrument cluster (A1) using the integral timer.
Reading in the data for the coolant temperature value:
- The coolant temperature sensor (B11/4) changes its resistance corresponding to coolant temperature. The sensor has an NTC resistance, i.e. the resistance reduces as temperature increases.
- 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 converted into a temperature value.
- This value is placed on the CAN-C by the motor electronics control unit (N3/10) or by the CDI control unit (N3/9).
The instrument cluster (A1) processes this data and drives the outside temperature indicator (A1p4) in the multifunction display (A1p13) accordingly.
The speed can also be displayed instead of the outside temperature in the multifunction display (A1p13). Changeover is effected in the "adjustments" menu.
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 value of 85 °C or 185 °F when the outside temperature is obviously lower, so there may be a short circuit in the sensor or in the line.
| Instrument cluster (IC), location/task | GF54.30-P-3039PP |