Fuel Gauge: Description and Operation

How the Circuit Works
The indicator lights come on under various conditions in their related systems. Refer to each related system to see the entire indicator light circuit.

Fuel Gauge and Low Fuel Indicator

WARNING: Do not smoke while working on the fuel system. Keep open flame away from the work area. Drain fuel only into an approved container.

The main circuit inside the gauge assembly monitors the resistance readings from the fuel gauge sending unit. Depending on the resistance value, the main circuit supplies a voltage to the coils inside the fuel gauge. The magnetic field causes the gauge needle to move. As the resistance in the sending unit varies, current through the gauge coils changes, moving the gauge needle toward the coil with the strongest magnetic field.

The fuel gauge sending unit's resistance varies from about 3 - 5 ohms at full to about 105 - 107 ohms at empty. When you turn the ignition switch to LOCK (0), the gauge remains at the last reading until you turn the ignition switch to ON (II) or START (Ill) again.

Voltage is supplied to the low fuel indicator through fuse 9 (in the driver's under-dash fuse/relay box). If the main circuit inside the gauge assembly senses that the resistance in the fuel gauge sending unit is too high (when the fuel level inside the fuel tank is too low) it will provide ground to the bulb, which turns on the low fuel indicator light.