Circuit Operation

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 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 volts 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, but less than 8 minutes, the oil level module ignores the low oil sensor.