Cherokee 4WD L6-4.0L VIN S (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 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.
