Grand Cherokee 2WD V8-5.2L VIN Y (1998)
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 decide 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.
