Gauges and Indicators

FUEL GAGE
The pointer of the Fuel Gage is moved by the magnetic fields of two coils. The coils are at right angles to each other. Battery voltage is applied to the F-coil and the circuit divides at the opposite end of the coil. One path continues to ground through the F-coil. Another goes to ground through the variable resistor of the Fuel Gage Sender.

When the tank is low, the resistance of the Sender is low. A large flow of current passes through the E-coil and the Fuel Gage Sender resistor. This moves the pointer toward E on the scale. When the tank is full, the Sender resistance is high. More current now flows through the F-coil, moving the pointer toward F on the scale.

With two coils operating the pointer, the Gage is not affected by changes in the system's battery voltage.


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 Oil Pressure Sender 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. The magnetic fields of the coils move the pointer from low to high.


TEMPERATURE GAGE
The 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 Engine Temperature Sender. This has 55 ohms resistance at 123°C (260°F) (hot coolant) and its resistance becomes greater at low temperatures. It is approximately 1400 ohms at 47°C (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's voltage with the Ignition Switch in RUN or START. With the engine stopped, the Voltmeter indicates Battery condition. With the engine running, the Voltmeter indicates Charging System operation.


ENGINE COOLANT LEVEL INDICATOR
The Engine Coolant Level Indicator comes on to warn the driver when a low level of coolant exists in the radiator. Battery voltage is applied to the Engine Coolant Level Indicator Module. When a low coolant condition exists, a signal is sent to the Engine Coolant Level Indicator Module from the Engine Coolant Level Sensor. The Engine Coolant Level Indicator Module will provide a ground to the Engine Coolant Level Indicator.

The Engine Coolant Level Sensor is not a switch that opens and closes. It has a very high resistance to ground, more that 50,000 ohms, when the engine coolant level is low. This causes the Engine Coolant Level Indicator Module to illuminate the Engine Coolant Level Indicator. With more of the Sensor covered by coolant, its resistance decreases. When the fluid level is good, the resistance will be less than 10,000 ohms. With the Sensor resistance between 10,000 and 50,000 ohms, the Sensor is partly covered and the fluid is not low enough to cause the warning to be displayed.


OIL PRESSURE INDICATOR

The Oil Pressure Indicator comes on to warn the driver when the engine oil pressure is low. Battery voltage is applied to one side of the bulb. A ground path is provided by the Oil Pressure Switch. It is closed when the oil pressure is below 27 kPa (4 psi). This tests the bulb when the Ignition Switch is turned on to start the engine. After the engine starts and normal oil pressure builds up, the Oil Pressure Switch opens. The Oil Pressure Indicator goes out.


SHIFT INDICATOR

With Manual Transmission, the SHIFT Indicator illuminates when the vehicle should be shifted to the next higher gear for better fuel economy. Battery voltage is applied to one side of the bulb. The other side of the bulb is switched to ground by the ECM/PCM which uses engine data such as rpm, vehicle speed and intake manifold vacuum to compute an efficient shift point.