Display speed, function - GF54.30-P-3025T
MODEL 211.0/2 up to 31.5.06 except CODE (494) USA version except CODE (498) Japan version
MODEL 211.0/2 up to 30.6.06 with CODE (494) USA version with CODE (498) Japan version
Networking
The electronic speedometer (A1p8) with its speedometer segment ring indicates the vehicle speed.
Speedometer arc
This is located in the second, passive level of the central display, which contains special areas that are activated to display the segments. The display of the speedometer segment ring comprises 52 segments in the ECE variants, 64 segments in the USA/UK variants which are visible on the inner edge of the speedometer scale.
On vehicles with model designation 211.067 and 211.267, the ECE variants and USA/UK variants each have 64 segments which are visible around the inner edge of the speedometer scale.
Measuring the vehicle speed
The speed is the distance traveled in kilometers or miles per hour. To calculate the vehicle speed, the processor in the instrument cluster (A1) evaluates the following wheel speeds:
- 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 instrument cluster (A1) receives the wheel speeds in RPM from the ESP control unit (N47-5) via the engine compartment CAN.
Speed limit (winter tires)
The speedometer segment ring is not displayed if a speed limit (from 160 km/h to 210 km/h in steps of 10 km/h or from 100 mph to 150 mph in steps of 10 mph) is activated via the 2nd operating level of the instrument cluster (A1).
Evaluating the wheel speed signals
Since not all of the wheels rotate at the same speed (when cornering), all four wheel speeds must be evaluated. The actual process is relatively complex, which is why only a general description is provided here:
The individual wheel speeds are compared and submitted to a plausibility check. If there are no significant differences, the vehicle speed is determined using the rotational speed of the left front wheel.
If the individual wheel speed signals differ considerably, the speed signals may be faulty or the vehicle may be cornering.
- If the processor's (lateral) comparisons of wheel speed indicate that the vehicle is cornering the speed is calculated from the average for both front wheels.
- If the comparisons indicate one or more incorrect wheel speeds, the speed is calculated from the highest wheel speed. This also applies if an error message is received instead of a rotational wheel speed. In this case, an appropriate error bit is stored in the memory.
Digital speedometer
The vehicle speed is displayed digitally. The default value for the display unit (km/h or miles/hr) is stored as a country-specific unit in non-volatile memory and can be changed via "Settings" in the Configurations/Settings menu item.
The digital speed display is matched to the speedometer display by a performance map. This ensures that the value of the analog needle position and the reading shown on the display are synchronized.
No speed display appears if error messages are received for all four wheel speeds. As the distance readings are also based on monitored speed, the odometer will cease to operate.
Depending on the national version, the electronic speedometer (A1p8) has a scale in kilometers per hour or a scale in miles per hour.
On vehicles with model designation 211.067 and 211.267, the scale of the electronic speedometer (A1p8) goes up to 320 km/h or 160 mph.
The tire size is taken into account when calculating the speed. Coding is performed using the Star Diagnosis tool.
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