RAM 2500 Truck 4WD V10-8.0L VIN W (1997)
Tachometer: Description and Operation
SYSTEM OPERATION
The tachometer gives an indication of the engine speed in revolutions-per-minute (rpm). The tachometer circuitry controls the gauge pointer
position. The proper gauge pointer position is calculated by the tachometer circuitry based upon an engine speed pulse signal received by the
tachometer from the Powertrain Control Module (PCM).
The PCM calculates the engine speed based upon an input from the crankshaft position sensor. The PCM then sends the proper pulse signal to the
tachometer circuitry. An electronic integrated circuit contained within the tachometer unit reads and analyzes this pulse signal. It then adjusts the
ground path resistance for one of the electromagnets in the gauge to control the tachometer needle movement.
The crankshaft position sensor is a hall-effect sensor installed on the engine, where it is aimed at a trigger wheel on the crankshaft. The frequency
values for the pulse signal are shown in a chart in Specifications.
CIRCUIT OPERATION
The tachometer module in the instrument cluster operates the tachometer. The Powertrain Control Module (PCM) supplies the signal for the
tachometer on circuit G21. Circuit G21 connects to cavity C31 of the PCM.