GF54.30-P-3019T Display Outside Temperature, Function

GF54.30-P-3019T Display Outside Temperature, Function

Component Identification:

Function requirements
The outside temperature display located in the right-side multifunction display (A1p13) indicates temperature based on the following information:
^ 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 controls the display accordingly. Due to the dependency of the outside temperature indicator in the multifunctional display (A1p13) on vehicle speed, engine running time and coolant temperature when the vehicle is stationary or driving slowly the system prevents too high a temperature being displayed as can be caused by radiated engine heat for example.

The display behaves differently according to the coolant temperature and the engine running time.

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

Coolant temperature ≥60 °C
As of circuit status "Circuit 15C ON" the temperature value measured last is stored and displayed for a maximum of 60 minutes. When the instrument cluster (A1) is activated the stored temperature value is displayed immediately. If the measured outside temperature falls below the stored value, the current measured temperature is displayed after 8 seconds. If the engine is off, the current outside temperature is displayed after six times the engine running time. In the process the preceding engine running time is taken as a basis, however for a maximum engine running time of 10 minutes.

Example
The preceding engine running time was 5 minutes. The delay period was then 6 times 5 minutes. The current temperature is thus only 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 thus 60 minutes.

When driving
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 of 20 km/h to 45 km/h rising outside temperatures are displayed after a delay period of 3 minutes. If the vehicle speed falls below 20 km/h, the display is only changed if the measured value falls.

Range
The display is -40 °C up to 85 °C or -40 °F up to 185 °F. The temperature is displayed in increments of 0.5 °C or 1 °F.

Changing over from degrees Centigrade to degrees Fahrenheit (up to 31.5.05)
The driver can switch between degrees Celsius and degrees Fahrenheit using the "Settings" function in the multifunction display (A1p13). The instrument cluster (A1) also sends a message for the air conditioning on the class B (interior) controller area network bus (CAN-B).

Temperature display (as of 1.6.05)
The outside temperature display can no longer be switched over between degrees centigrade and degrees Fahrenheit. The temperature display is determined via the variant coding in the central gateway control unit (N93).

Data for outside temperature
The outside temperature indicator temperature sensor (B14) changes its resistance according to the outside temperature. The sensor is a resistor which reduces its resistance as temperature increases. The resistance value of the outside temperature display temperature sensor (B14) is read in by the driver-side SAM control unit with fuse and relay module (N10/1) The driver-side SAM control unit with fuse and relay module (N10/1) converts the resistance value from the outside temperature indicator temperature sensor (B14) into a temperature value. This temperature value is placed on the CAN B by the driver-side SAM control unit with fuse and relay module (N10/1).

Vehicle speed signal
The following signals are read in by the SBC control unit (A7/3n1):
^ Left front rpm sensor (L6/1)
^ Right front rpm sensor (L6/2)
^ Left rear rpm sensor (L6/3)
^ Right rear rpm sensor (L6/4)

The SBC control unit (A7/3n1) places the 4 wheel speed signals on the Controller Area Network bus class C (engine compartment) (CAN-C) via the ESP control unit (N47-5). The instrument cluster (A1) uses these signals to calculate the speed.

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 read by the CDI control unit (N3/9) or the ME-SFI control unit (N3/10). The ME control unit (N3/10) or CDI control unit (N3/9) converts the resistance values from the coolant temperature sensor (B11/4) into a temperature value. This temperature value is placed on the CAN C by the CDI control unit (N3/9) or ME-SFI [ME] control unit (N3/10).

Engine running time
The engine running time is calculated internally in the instrument cluster (A1) using the integral timer. The instrument cluster (A1) processes this data and controls the display accordingly.

Notes on diagnosis
If the display shows the lower temperature value -40 °C or -40 °F with a temperature value which is evidently higher, there may be a sensor fracture or cable open circuit. If the display indicates the maximum temperature value 85 °C or 185 °F although the actual outside temperature is obviously lower, this could indicate a short circuit in the sensor or in the line.

If the coolant temperature sensor (B11/4) is defective and a valid coolant temperature is not passed on from the CAN-C, processing moves to the range for coolant temperature 60 °C.