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.