For 1990-2009 cars

### Circuit Operation

The operation of each circuit is described with the corresponding circuit description.

### Fuel Gauge (Oldsmobile)

The magnetic field of the 2 coils moves the pointer of the fuel gauge. The coils are at right angles to each other. Battery voltage is applied to the F coil. The circuit divides at the opposite end of the coil. Another circuit goes through the variable resistor of the fuel gauge sensor.

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 gauge sender resistor. This moves the pointer toward E on the scale. When the tank is full, the sender resistance is high. More current flows through the F coil. This moves the pointer toward the F on the scale.

With 2 coils operating the pointer, the gauge is not affected by changes in the vehicle's electrical system.

The Oldsmobile gauges cluster (UH8) uses a fuel antislosh system that needs to be reset in order to get an immediate reading of the gauge. This fuel antislosh circuit is reset by cycling the ignition switch from OFF to ON.

### Fuel Gauge (Buick, Pontiac)

The magnetic fields of the 2 coils move the fuel gauge pointer. The coils are at right angles to each other. The 2 coils are connected to each other. The fuel level Pulse-Width Modulated (PWM) circuit from the PCM connects at a middle point. Battery voltage is applied to the end of the coil at the E end. Ground is applied at the other coil's F end.

The fuel level sender resistance is proportional to the fuel level. The voltage across the sender is the fuel level input signal that is applied to the PCM on CKT 30 and CKT 452. The PCM provides a Pulse-Width Modulated (PWM) fuel level output signal on CKT 455 (PPL/WHT) to the instrument cluster fuel gauge.

When the tank is low, the fuel level sender resistance is low. A larger current passes through the E coil in order to move the pointer toward E on the scale. When the tank is full, the sender resistance is high. More current flows through the F coil. This moves the pointer toward F on the scale.

With 2 coils operating the pointer, the gauge is not affected by changes in the vehicle's electrical system.

### Oil Pressure Gauge

The oil pressure gauge displays the engine oil pressure. The pointer of the gauge is moved by 2 coils. The oil pressure gauge is similar to that of the fuel gauge.

The oil sensor/switch is connected to the junction of the 2 coils. The sensor has low resistance when the oil pressure is low and 90 ohms resistance when the pressure is high. This changing resistance changes the current flow through the coils. The coil's magnetic fields move the pointer from high to low.

### Coolant Temperature Gauge

The coolant temperature gauge is also operated by 2 coils. Battery voltage is applied to both coils. One coil is grounded directly and the other coil is grounded through the engine coolant temperature (ECT) sensor. The ECT has 55 ohms resistance at 127°C (260°F). The resistance becomes greater at low temperatures. The resistance is approximately 1400 ohms at 38°C (100°F). This causes the current through the sensor 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 the following positions:

• | RUN

• | BULB TEST

• | START

When the engine is stopped, the voltmeter indicates battery condition. When the engine is running, the voltmeter indicates charging system operation.

### Speedometer and Odometer

An electronic circuit operates the speedometer. The vehicle speed sensor (VSS), located in the transaxle, generates an ac voltage with a frequency proportional to the speed of the vehicle. The voltage goes to the powertrain control module (PCM) and then to the speedometer circuit board in the instrument cluster. The solid state unit drives the pointer of the speedometer.

The same buffered speed signal from the PCM is processed by the speedometer circuit board in order to drive the odometer. The odometers are operated by a stepper motor that responds to pulses from the speedometer circuit.

### Boost Gauge (Pontiac with U2F)

The boost gauge is available only with the Pontiac U2F gages cluster. The boost gauge displays the engine intake manifold vacuum or the pressure. This indicates the proper operation of the supercharger.

The boost gauge is an electrically-controlled air core display that receives input from the boost/manifold absolute pressure (MAP) sensor as a variable voltage proportional to the manifold vacuum or the pressure.

### Tachometer

The tachometer displays the engine speed. The tachometer is an electrically-controlled direct drive display that receives the engine speed input from the ignition control module (ICM)