Tuesday, December 18, 2018

Instruments - Maximum Permissible Speedometer Deviations

For information only 2010 BMW 335Cic Convertible (E93) L6-3.0L Turbo (N54) Technical Service Bulletin # 620612 Date: 120401



Instruments - Maximum Permissible Speedometer Deviations



SI B62 06 12



Instruments



April 2012



Technical Service



This Service Information bulletin replaces SI B62 02 96.



SUBJECT



Maximum Permissible Speedometer Deviations



MODEL



All



SITUATION



The vehicle speed displayed in the instrument cluster displays a speed that is higher than the actual speed.



INFORMATION



Most speedometers have tolerances of approximately +10%. A "speedometer advance" is necessary to compensate for negative tolerances in tire



diameter, electronic controls, tire temperature, tire pressure, vehicle load and other factors.



Vehicle manufacturers usually calibrate speedometers to read high by an amount equal to the average error, to ensure that their speedometers never



indicate a lower speed than the actual speed of the vehicle.



Excessive speedometer deviations can come from several causes, but most commonly are due to nonstandard tire diameter and wheel size.



This SI defines the maximum and permissible speedometer reading tolerance.



The instrument cluster is a sealed unit and cannot be calibrated. Any tampering to the cluster will void the related component or vehicle warranty



coverage that is applicable.



2010 BMW 335Cic Convertible (E93) L6-3.0L Turbo (N54) 64



GPS devices are positional speedometers, based on how far the receiver has moved since the last measurement. Its speed calculations are not subject



to the same sources of deviation as the vehicle's speedometer (wheel size, transmission/drive ratios). Instead, the GPS positional accuracy, and



therefore the accuracy of its calculated speed, is dependent on the satellite signal quality at the time.



If you are using a known accurate GPS system as a reference speed, you need to use the formula below to calculate the maximum permitted



speedometer advance, which is 10% of the actual (input) speed plus 2.4 mph.



Example:



Actual speed = 50 mph



50 mph x 10% = 5 mph; 5 mph + 2.4 mph = 7.4 mph



Therefore, the permissible displayed speed is 50 to 57.4 mph.



(Note: The displayed speed must never be less than the actual speed.)



No repairs should be attempted if the speedometer advance is within 10% + 2.4 mph.



Use ISTA ((Integrated Service Technical Application) diagnosis or the instrument cluster self-test to make sure the needle for the speedometer is



moving smoothly.



NOTE:



The amount of speedometer advance has no effect on recording accumulated mileage in the odometer display. The odometer records total mileage



digitally, and does not incorporate any "advance" tolerances.

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