For 1990-2009 cars

### Circuit Operation

The instrument cluster contains analog gauges and indicators. Some of the gauges and indicators are controlled by solid-state controls within the cluster. The other gauges and indicators are controlled by direct circuits into the cluster from other components. These operations are described here briefly.

### "ABS INOP" Indicator

Refer to Antilock Brake System.

### "AIR BAG" Indicator

Refer to Supplemental Inflatable Restraints.

### "ASR" Indicator (Chevrolet)

Refer to Antilock Brake System.

### "BRAKE" Indicator

Refer to Brake Warning System Circuit Description .

### "CHECK GAUGES" Indicator

The instrument cluster's internal circuitry monitors three inputs for determining when to illuminate the "CHECK GAUGES" indicator.

A ground is provided inorder to illuminate the "CHECK GAUGES" indicator when the follwing conditions exist:

1. The coolant temperature sensor indicates above-normal temperature (252°F for V6 VIN K or 244°F for V8 VIN G).
2. The instrument cluster senses that the generator turn-on input is at ground potential. The generator pulls CKT 225 low when any of the following conditions exist:

• | System voltage at or below 11.2V.

• | System voltage is at or above 16.5V.

• | The generator is stopped.

3. The oil pressure sensor indicates below-normal pressure. The minimum rating for the pump is 8.3 psi, though the sensor will be approximately 3 to 5 psi at 10ohms. This situation will cause the "CHECK GAUGES" indicator to illuminate (maximum pressure should be about 90ohms at the sensor).
4. The instrument cluster performs a bulb check function for approximately one second after the ignition is turned ON.

### Coolant Temperature Gauge

The coolant temperature gauge contains internal coils that create magnetic fields when current flows through the coils. The current through the coils varies depending on the coolant temperature sensor resistance (approximately 55ohms at 260°F (hot) and approximately 1365ohms at 100°F). The varying sensor resistance causes the current through the coils to fluctuate. The magnetic fields of the coils move the pointer.

### "FASTEN SEAT BELT" Indicator

Refer to Audible Warnings Circuit Description .

### Fuel Gauge

The fuel gauge needle deflects from empty to full based on the output the needle receives from a solid state module. This module is also located within the instrument cluster. The module receives a pulse width modulated signal from the Powertrain Control Module (PCM). This signal varies based on the amount of fuel the fuel level sender detects in the vehicle fuel tank. For further information regarding the fuel gauge, refer to Engine Controls.

### High Beam Indicator

System voltage is applied to the high beam indicator whenever the following conditions exist:

1. The headlights are ON.
2. The headlight dimmer switch is on HIGH.

The indicator has a constant ground and illuminates whenever system voltage is applied.

### "LOW COOLANT" Indicator (V8 VIN G)

The "LOW COOLANT" indicator has system voltage applied in "RUN", "BULB TEST" or "START". The indicator requires a ground for illumination. Following are two ways that the indicator receives a ground:

• | During the bulb check through the instrument cluster

• | Whenever the engine coolant level sensor detects a low coolant condition

The instrument cluster performs a bulb check by grounding the circuit to the indicator for approximately one second after the ignition is turned ON. When a low coolant condition occurs, a ground path is supplied through the engine coolant level sensor to the indicator. At the same time, ground is suppled through the engine coolant level sensor to the Body Control Module (BCM). The module is designed to provide a continuous ground path to the indicator for the remainder of the ignition cycle in which a momentary low coolant condition occurred. The module provides its own ground to the indicator until the ignition switch is turned OFF.

### "LOW OIL" Indicator

The instrument cluster's internal circuitry will only test the oil level sensor at the ignition ON if drainback times are met as follows:

• | 35 minutes after ignition OFF if the engine was still cold.

• | 4 minutes after ignition OFF if the engine was hot (running for at least 17 minutes).

The drainback timer sets at ignition OFF. The sensor has normally closed contacts that are open under a low oil condition. After determining that a low oil condition exists, the "LOW OIL" indicator is provided a ground for illumination. The indicator also receives a ground for approximately one second during the cluster's bulb check function right after ignition ON. For further information regarding the "LOW OIL" indicator, refer to Engine Controls.

### "LOW TRAC" Indicator

Refer to Antilock Brake System.

### Odometer

Voltage that pulses from the Powertrain Control Module (PCM) on CKT 817 is interpreted by solid state logic circuits within the cluster. The solid state circuits process the pulses and output a signal to drive the odometer. The odometer is pre-set to display distance traveled in either miles or kilometers and cannot be changed.

### Oil Pressure Gauge

The oil pressure gauge contains internal coils that create magnetic fields when current flows through the coils. The current through the coils varies depending on the oil pressure sensor resistance as follows:

• | Low pressure resistance is approximately 10ohms.

• | High pressure resistance is approximately 90ohms.

The varying sensor resistance causes the current through the coils to fluctuate. The magnetic fields of the coils move the pointer.

### "SECURITY" Indicator

Refer to Vehicle Theft Deterrent (VTD) Operation .

### "SKIP SHIFT" Indicator

Refer to Engine Controls.

### (MIL) "SERVICE ENGINE SOON" Indicator

Refer to Engine Controls.

### Speedometer

The speedometer displays vehicle speed in miles per hour (MPH) or kilometers per hour (KPH). Voltage pulses from the Powertrain Control Module (PCM) are interpreted by solid state logic circuits within the cluster. The solid state circuits process the pulses and output a signal to drive the speedometer pointer. For further information regarding the speedometer, refer to Engine Controls.

### Tachometer

The tachometer displays engine speed in Revolutions Per Minute (RPM). Voltage pulses from the electronic ignition control module (V6 VIN K) or the powertrain control module (V8 VIN G) are interpreted by solid state logic circuits within the cluster. The solid state circuits process the pulses and put out a signal that drives the pointer of the meter. The pointer is moved with magnetic fields created from coils within the tachometer.

### "TCS OFF" Indicator (Pontiac)

Refer to Antilock Brake System.

### Voltmeter

The voltmeter measures the vehicle's electrical system voltage during run or stopped conditions. The voltmeter has two coils internally that create magnetic fields. These coils are made of a different amount of windings and are in series with a calibrated resistance. Any voltage between 8 to 18 volts will create a magnetic field that will move the pointer to the appropriate voltage indication.