Gages

Only those indicators and gages that are not described in connection with other circuits are explained in this circuit operation. See the circuit referred to for its complete operation.

TACHOMETER

The Tachometer displays engine speed in rpm. Voltage pulses are taken from the Ignition System and sent to the Tachometer. it responds to the frequency of the voltage pulses which increase with engine speed. Solid state circuits process these pulses into a signal that drives the pointer of the meter.

FUEL GAGE

The Fuel Gage receives a variable resistance signal from the Fuel Gage Sender which is directly related to the amount of fuel in the fuel tank. This variable resistance is an analog signal which is processed by the instrument Clusters electronics to produce a digital value from 1 to 14 bars. A resistance of 15 ohms will cause 1 bar to light and flash while 90 ohms will light all 14 bars. The gage is a liquid crystal display (LCD).

OIL PRESSURE GAGE

The engine oil pressure is displayed by the Oil Pressure Gage. The pointer of the gage is moved by two coils, and its operation is similar to that of the Fuel Gage.

The Fuel Pump/Oil Pressure Sender/Switch is connected to the junction of the two coils. it has low resistance when the oil pressure is low, and 90 ohms resistance when the oil pressure is high. This changing resistance changes the current flow through the coils to move the pointer from 0 to 80 psi.

COOLANT TEMPERATURE GAGE

The Coolant Temperature Gage is also operated by two coils. Battery voltage is applied to both coils. One is grounded directly and the other is grounded through the Coolant Temperature Sender.This has 60 ohms resistance at 280°F (hot coolant) and its resistance increases at lower temperatures. Resistance is approximately 1400 ohms at 100°F. This causes the current through the Sender and one coil to increase as the coolant temperature increases. This moves the pointer.

VOLTMETER

The Voltmeter measures the electrical system voltage with the Ignition Switch in RUN, BULB TEST or START. With the engine stopped the Voltmeter indicates Battery condition. With the engine running, the Voltmeter indicates Charging System operation.

SERVICE ENGINE SOON INDICATOR

The SERVICE ENG. SOON Indicator serves as a warning light to tell the driver that a problem has occurred and that the car should be serviced. It is also used by the technician to read out diagnostic codes to help diagnose system problems.

The indicator receives battery voltage in RUN, BULB TEST and START. The ECM provides a switched path to ground.

LOW COOLANT INDICATOR

The Low COOLANT Indicator comes on to warn the driver when the level of coolant in the radiator is low. Battery voltage is applied in BULB TEST and START. The ECM provides a switched path to ground.

SPEEDOMETER AND ODOMETER DISPLAYS

The Vehicle Speed Sensor (VSS) generates a signal that indicates the speed of the vehicle. The signal is processed by the solid state ECM to supply inputs to the Trip Computer, Cruise Control Module, Speedometer and Odometer.

The Vehicle Speed Sensor is mounted in the transaxle. A magnet rotates near a coil, producing voltage pulses in the coil. The frequency of the AC voltage coming from this coil depends on the vehicle speed. The VSS sends pulses to the ECM at the rate of 40,000 pulses per mile.

The ECM takes the voltage pulses from the sensor and uses them to close a solid state output switch. The output terminal is switched to ground at a rate that is proportional to the speed of the car. The Speedometer and odometer are switched at 4,000 pulses per mile.

COOLANT TEMPERATURE INDICATOR

Battery voltage is applied to the Coolant Temperature Indicator in RUN. The Coolant Temperature Indicator is tied to the Coolant Temperature Sender through solid state indicator control circuitry located in the Instrument Cluster. This indicator control circuit monitors the resistance of the Coolant Temperature Sender. When the resistance of the sender reaches approximately 60 ohms (280°F, 137°C) the indicator control unit grounds the Coolant Temperature indicator causing this indicator to light.

OIL PRESSURE INDICATOR

Battery voltage is applied to the Oil Pressure Indicator in RUN. The Oil Pressure Indicator tied to the Oil Pressure Sender through solid state indicator control circuitry located in the Instrument Cluster. This indicator control circuit monitors the resistance of the Oil Pressure Sender. When the resistance of the sender reaches approximately 4 ohms (4 PSI, 27 kPa the indicator control unit grounds the oil pressure indicator causing this indicator to light.