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Home >> Mercedes Benz >> 2004 >> C 230 CL (203.740) L4-1.8L SC (271.948) >> Repair and Diagnosis >> Instrument Panel, Gauges and Warning Indicators >> Description and Operation >> GF54.30-P-3019PM Displaying Outside Temperature, Function

GF54.30-P-3019PM Displaying Outside Temperature, Function




GF54.30-P-3019PM Displaying Outside Temperature, Function
- MODEL 203.0 /2 /7 as of 24.4.04 up to Model Year 8






A1 Instrument cluster
A1p4 Outside temperature indicator
B11/4 Coolant temperature sensor
B14 Outside temperature display temperature sensor
L6/1 Left front rpm sensor
L6/2 Right front rpm sensor
L6/3 Left rear rpm sensor
L6/4 Right rear rpm sensor
N3/9 CDI control unit
N3/10 ME-SFI [ME] control unit
N10/1 Front SAM control unit with fuse and relay module
N47-5 ESP and BAS control unit

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.

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

Coolant temperature ≥60 °C
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.
When driving the delay periods also depend on the vehicle speed:
- At speeds of 20 to 45 km/h rising outside temperature are displayed after a delay period of t = 3 minutes.
- At speeds > 45 km/h rising outside temperatures are displayed after a delay period of t = 1.5 minutes.
- With a reduction in speed < 20 km/h the display is only changed when the measured outside temperature value drops.

When the instrument cluster (A1) does not receive a valid coolant temperature from the CAN-C, the method opposite for coolant temperature ≥60 °C is used to determine the outside temperature.

Rising outside temperature when engine is not running
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.

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 a negative temperature coefficient (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 a negative temperature coefficient 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.

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 t he multifunction display (A1p13).

Range
The display range is -40 to +85 °C or -4 0 to +185 °F. The temperature is displayed in increments of 0.5 °C or 1 °F. If the outside temperature measured exceeds the display range the maximum display value of the display range is shown. If the outside temperature measured drops below the display range, the minimum display value of the display range is shown.

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.




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