Tachometer: Description and Operation

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 a hall-effect sensor installed near the rear of the engine, where it is aimed at the trigger wheel attached to the rear flange of the crankshaft.

Refer to Powertrain Managemen/Computer and Control System for more information on the PCM. Refer to Powertrain Management/Computer and Control System for more information on the crankshaft position sensor.