Gauges and Indicators

SPEEDOMETER/ODOMETER
The speedometer receives vehicle speed information from the Powertrain Control Module (PCM). The vehicle speed signal is passed through an RC filter to the input of the speedometer/odometer drive integrated circuit (IC), located in the instrument cluster. The high-to-low edge of the square wave input triggers the IC to produce a well defined pulse of current to the moving coil inside the speedometer gauge. The IC also counts the input transitions and uses this information to drive the stepper motor for both the odometers. The vehicle completes one mile for every 4983 pulses received from the PCM.


TACHOMETER
The tachometer receives engine RPM information from the Distributorless Ignition System (DIS) module. The engine RPM signal is buffered by an RC filter/limiting diode and sent to the tachometer drive integrated circuit (IC), both located within the instrument cluster. The IC receives a low-to-high square wave signal, and produces a well defined pulse of current to the moving coil inside the tachometer. The engine completes one revolution for every two pulses received from the DIS module.

TEMPERATURE GAGE
The temperature gage receives a variable resistance signal from the coolant temperature gauge sender. This variable resistance regulates the current through the coil windings of the temperature gauge, which in turn deflects the gauge pointer. The current for the gauge is supplied by the cluster, when the ignition switch is in the RUN and CRANK position.

FUEL GAGE
The fuel gage receives a variable resistance signal from the fuel sender, located in the fuel tank. This signal is a function of the amount of fuel remaining in the tank. This variable resistance regulates the current through the coil windings of the fuel gage, which in turn deflects the gage pointer. The current for the gage is supplied by the cluster, when the ignition switch is in the RUN and CRANK position.