Electronic Tachometer

Testing electronic tachometer

Note:

The electronic tachometer (E-tacho) comprises an inductance transmitter on transmission and an indicator in instrument cluster.




The inductance transmitter on transmission translates the speed of the transmission main or input shaft into an electric signal. The number of signal impulses is in accordance with vehicle speed. The signals are converted in tachometer into a mechanical readout (speed and odometer).




On vehicles with automatic transmission the inductive transmitter (1) is combined in a harness together with the electric connections of starter lockout and backup lamp switch and can be exchanged only complete with harness.

If the E-tacho does not indicate, the following checkup can be made for diagnosis "inductive transmitter with line" or "E-tacho" defective.


Checkup

1 Remove inductive transmitter on transmission, unscrewing screw M 6 on inductive transmitter for this purpose and pull out inductive transmitter.




2 Switch on ignition. Place a wide screwdriver against underside of transmitter.




3 Pull off screwdriver with quick movements and put back again.

This fast pulling and pulling back will generate a signal on intact transmitter which will cause the tachometer needle to perform a slight deflection.




4 If not, remove instrument cluster and pull off 4-point coupler (2).




5 Connect a voltmeter (measuring range 0-3 volts, AC) to jack 1 and 3 and repeat test.

If the needle on voltmeter deflects when the screwdriver is pulled away from transmitter, the transmitter with its line is in order and the E-tacho is defective. If the needle is not deflecting, the transmitter is defective or the line to instrument cluster is interrupted.