Functional Description

Functional Description

The rev counter signal is supplied to the instrument cluster:

for the Petrol version: by the engine injection/ignition control unit S11/S40 which processes an "rpm" signal thanks to sensor S31.

The signal reaches the cluster C10 at pin 2 of connector A, leading from connector G133a which connects the injection/ignition system with the other circuits; inside the cluster it then reaches the electronic device that operates the rev counter.

for the TD version: from the special sensor L16 fitted on the flywheel ring gear so that it can constantly read the engine rpm.

The sensor is inductive and detects the engine rpm through the change in a magnetic field produced by the passage of the teeth of the flywheel ring gear. The signal reaches the instrument cluster C10 at pin 2 of connector A, leading from sensor L16; inside the cluster it then reaches the electronic device that operates the rev counter.

The same signal is then sent to the heating and ventilation system, to the compressor cut-out control unit Q67.

The speedometer signal is supplied by the speedometer sensor L17: this is fitted on the gearbox and detects the speed of the car at all times.

This device is a pulse generator which generates and processes a signal that is proportionate with the speed of the camshaft at the gearbox output, therefore with that of the wheels: it is a "square-wave" signal obtained:

for the Petrol versions: through an electronic module, inside the actual sensor, which "squares" a sinusoidal signal captured by a magnetic core.

for the TD version: it is a Hall effect sensor which processes the output signal.

The sensor L17 is supplied at pin 3 with stabilised voltage through an electronic device inside the instrument cluster (from pin 5 of connector A of C10); pin 1 is connected to earth G53b, while the tachometric signal (proportionate with the speed of the car leaves pin 2 and is sent to the instrument cluster C10 at pin 11 of connector A, and from here to the electronic device that operates the speedometer and the two mileage recorders (total and trip).

The same signal is also sent - for the Petrol versions - to the injection/ignition system which needs the "car speed" information (see the corresponding sections).