Simulating Vehicle Speed Signal

Image Legend:
1 FREQ ON (-), black
2 FREQ ON (+), yellow
3 Speed A wire or instrument cluster - rear axle reed contact wire
4 Simulator for instrument cluster
5 Jumper

Simulating vehicle speed signal:

Measuring instrument: BMW simulator for instrument cluster and BMW SERVICE TESTER

Test leads: FREQ ON (+), yellow; FREQ ON (-); Special connection lead Cartool No.61 2 020 for frequency simulation

Test Procedure:

The speed signal can be set continuously variable with the BMW simulator for the instrument cluster.

Connect Cartool special connection lead for frequency simulation to the simulator. Connect the power supply lead of the simulator to the vehicle battery. Connect the frequency lead of the simulator to the vehicle wire for the speed signal (speed A wire or wire at rear axle reed contact; disconnect plug-and-socket connection!). Set frequency on the simulator.

The frequency can also be measured by means of the BMW SERVICE TESTER:

Connect the black FREQ ON (-) terminal to chassis ground and the yellow FREQ ON (+) terminal to the frequency output of the simulator.

Select *M* for multimeter and "14" frequency test, the set frequency is indicated.

Important!

Simulation of the speed signal results in a defect code being stored in some control units. For this reason, perform a quick-test on completion of the signal test and clear the defect codes stored by the simulation.

Calculation of the Vehicle Speed:

General

The speed v can be calculated with the aid of the entered frequency f (in Hz) and the K-number (or read out via the system tester!).

The K-number already contains the conversion to km/h or mph, i.e. the K-number of a km/h speedometer provides the speed v in km/h, and the K-number of a miles speedometer in mph.

The following formula is used to calculate the speed v:

v = f x 3600/ K-number

Deviation:

The speedometer value may be up to 10% above the calculated value (speedometer advance).

Example:

A frequency f = 200 Hz and the K-number 4535 from a kilometer speedometer result in:

v = 200x3600/4535 = 159,

The speed is therefore 159 km/h.