Circuit Operation - Gauges Cluster

The operation of an individual indicator is described along with its circuit. Refer to the schematic and text for the circuits described below.

Fuel Display
The fuel level sensor provides a signal to the instrument cluster that is related to the fuel level. With a full tank, the fuel gage sender resistance is 88 ohms; with an empty tank, the resistance is near 0 ohms. The instrument cluster electronics converts the analog signal from the fuel gage sender to a digital signal that controls the air core fuel gage display.

Temperature Display
The instrument cluster receives engine coolant temperature data from the PCM over the serial data link. Engine coolant temperature is then displayed to the driver by an air core display.

Speedometer And Odometer
The Vehicle Speed Sensor (VSS) generates a signal that indicates the vehicle speed. The signal is processed by the solid state Powertrain Control Module (PCM) to supply inputs to the speedometer and the odometer.

The vehicle speed sensor is mounted in the transaxle, and generates an AC voltage signal with a frequency proportional to vehicle speed.

The PCM takes the voltage pulses from the sensor and translates the signal to a 4000 pulses per mile signal for the IPC. The output terminal is switched to ground at a rate that is proportional to vehicle speed. The speedometer and odometer are switched at the same frequency that the sensor generates.

The speedometer and odometer are operated by a circuit board in the cluster. This circuit board converts the pulses received from the PCM into a control signal for the air core and vacuum fluorescent displays (Buick) or stepper motors (Oldsmobile).

Check Oil Level Indicator
The CHECK OIL LEVEL indicator is lit to alert the driver of a low oil level condition. The low oil sensing circuit consists of an oil level module and low oil level sensor. This system is active only at initial engine starting and not while the engine is running. The oil level is measured if the engine has been off long enough for top engine oil to have returned to the oil pan.

The oil level module receives battery power at all times to retain memory of engine on and off times. If the ignition on input as been at 0 volt for at least 8 minutes, the oil level module activates the low oil level sensor. If the sensor returns a signal indicating a low oil condition, the cluster lights the CHECK OIL LEVEL indicator 15 to 25 seconds after the ignition switch is turned to "RUN." If the ignition switch is turned off for less than 20 seconds, the oil level module remembers and sends the previous oil level status to the cluster and ignores the present oil status. If the ignition switch has been "OFF" for more then 20 seconds, hut less than 8 minutes, the oil level module ignores the low oil sensor.

Low Coolant Indicator (BUICK ONLY)
Coolant level information 5 received from the oil level module and the low coolant sensor. If the low coolant sensor returns a signal indicating a low coolant condition, the cluster lights the LOW COOLANT indicator.

Low Washer Fluid Indicator (BUICK ONLY)
Low washer fluid information is received from the Washer Fluid Level Switch. The Washer Fluid Level Switch provides an ignition feed when the washer fluid is low and the Wiper Washer Switch is placed in the washer position.