Tachometer

TACHOMETER-PCM OUTPUT

The Powertrain Control Module (PCM) supplies engine rpm values to the instrument cluster tachometer through the PCM's CCD (Information) bus circuits. Refer Instrument Panel and Gauges for tachometer information.

SYSTEM OPERATION
The tachometer gives an indication of the engine speed in revolutions-per-minute (rpm). The instrument cluster circuitry controls the gauge pointer position. The instrument cluster circuitry calculates the proper gauge pointer position based upon an engine speed message received from the Powertrain Control Module (PCM) on the Chrysler Collision Detection (CCD) data bus.

The PCM uses an input from the crankshaft position sensor and internal programming to calculate what engine speed message is required. The PCM then sends the proper message to the instrument cluster on the CCD data bus.

The crankshaft position sensor is installed near the rear of the engine, where it is aimed at the trigger wheel attached to the rear flange of the crankshaft.

CIRCUIT OPERATION
The Powertrain Control Module (PCM) broadcasts the engine RPM data on the CCD bus. From the RPM message on the CCD bus, the instrument cluster calculates tachometer needle position.