GM Service Manual Online
For 1990-2009 cars only

Fuel Gauge

The pointer of the fuel gauge is moved by the magnetic fields of two coils. The coils are at right angles to each other. The voltage is applied to coil F from the IG-COIL fuse. The circuit divides at the opposite (ground) side of the coil. One path seeks a ground through the variable resistor in the fuel level sensor.

When the fuel level is low, the resistance in the fuel level sensor is high. Since the current will always seek the path of least resistance, the current will flow through coil F and coil E to ground at G 105. The E coil winding is twice the length of the F coil winding. Because of this, the magnetic field generated by the E coil is twice as strong as the magnetic field generated by the F coil. Therefore, the pointer may pull to the E position.

As the fuel level increases, the resistance in the fuel level sensor decreases. Because the current always seeks the path of least resistance, more current will begin to bypass the E coil and travel directly to ground through the fuel level sensor. Under these conditions, the coil F magnetic field becomes stronger than the coil E magnetic field. The pointer moves toward the F position.

Engine Coolant Temperature Gauge (ECT)

The pointer of the ECT gauge is moved by the magnetic fields of two coils. The coils are at right angles to each other. The voltage is applied to coil H from the IG-COIL fuse. The circuit divides at the opposite (ground) side of the coil. One path seeks a ground through coil C. The other path seeks a ground through the variable resistor in the Engine Coolant Temperature (ECT) Sensor.

When the engine coolant temperature (ECT) is low, the resistance in the ECT sensor is high. Because the current always seeks the path of least resistance, the current flows through the H coil and the C coil to ground at G 105. Because the length of the C coil winding is twice the length of the H coil winding, the magnetic field generated by the coil C is twice as strong as the magnetic field generated by the coil H. Therefore, the pointer may be pulled to the C position.

As the ECT increases, the resistance in the ECT sensor decreases. Because the current always seeks the path of least resistance, more current begins to bypass the C coil, traveling directly to the ground through the ECT sensor. Under these conditions, the coil H magnetic field becomes stronger than the coil C magnetic field. The pointer moves toward the H position.

Oil Pressure Indicator

The battery voltage is applied through the IG-COIL when the ignition switch is in the following positions:

    • ON
    • START

Fuse the oil pressure indicator in the IP cluster assembly. If the engine oil pressure falls below 31 kPa (4.5 psi), the oil pressure switch located in the cylinder block closes. When the oil pressure switch is closed, the following conditions may occur:

    • A path is provided to the oil pressure indicator.
    • The bulb lights.

Tachometer

The tachometer displays the engine speed in rpms. Ground pulses are taken from the ignition system and sent to the tachometer. The tachometer responds to the frequency of the ground pulses. This increases with the engine speed.