Indicators Cluster

CIRCUIT OPERATION
The Instrument Cluster contains Analog Gages and Indicators. Some Gages and Indicators are controlled by solid state controls within the Cluster; some are controlled by direct circuits into the Cluster from other components. These operations are described here briefly.

"ABS INOP" INDICATOR, FOR Z49:
See "Antilock Brakes" under Brakes & Traction Control.

"AIR BAG" INDICATOR
See "Air Bags & Seat Belts".

"BRAKE" INDICATOR, FOR Z49:
See "Brake Lamp" (Warning Indicator) Brake Warning Indicator

"CHECK GAUGES" INDICATOR
The Instrument Cluster's internal circuitry monitors three inputs for determining when to illuminate the "CHECK GAUGES" Indicator.

The "CHECK GAUGES" Indicator is provided a ground for illumination when:
1. The Coolant Temperature Sensor indicates above normal temperature (252°F for V6 VIN S or 244°F for V8 VIN P).
2. The Instrument Cluster senses the Generator turn on input is at ground potential. The Generator pulls CKT 225 low with system voltage at or below 11.2v or with 16.5v or higher, also pulled low if Generator is stopped.
3. The [1][2]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 10 ohms which will cause the "CHECK GAUGES" Indicator to illuminate (maximum pressure should be about 90 ohms at the sensor).
4. The Instrument Cluster performs a bulb check function for approximately one second after Ignition "ON."

COOLANT TEMPERATURE GAGE
The Coolant Temperature Gage contains internal coils that create magnetic fields when current flows though them. The current through the coils varies depending on the Coolant Temperature Sensor resistance [approximately 55 ohms at 260°F (hot) and approximately 1365 ohms 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
See "Audible Warning Device" Audible Warning Device

FUEL GAGE
The Fuel Gage contains internal coils that create magnetic fields when current flows through them. The current through the coils varies depending on the Fuel Gage Sender resistance (see Fuel Level/Resistance Chart). The varying sender resistance causes the current through the coils to fluctuate. The magnetic fields of the coils move the pointer.

HIGH BEAM INDICATOR
The High Beam Indicator has system voltage applied to it whenever the Headlights are "ON" and the Headlight Dimmer Switch is on "HIGH." The Indicator has a constant ground and will illuminate whenever system voltage is applied.

"LOW COOLANT" INDICATOR (V8 VIN P)
The "LOW COOLANT" Indicator has system voltage applied in "RUN," "BULB TEST" or "START." The Indicator requires a ground for illumination. There are two ways the Indicator receives a ground:
1. During "BULB TEST" through the Ignition Switch.
2. Whenever the Engine Coolant Level Sensor detects a low coolant condition.

When a low coolant condition occurs, a ground path is supplied through the Engine Coolant level Sensor, and the Isolation Diode to the Indicator. At the same time, ground is supplied through the Engine Coolant Level Sensor to the Low Coolant Relay. The Low Coolant Relay 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 relay provides its own ground to its coil and to the Indicator until the Ignition is turned "OFF." This is called latching.) The purpose of the Isolation Diode is to prevent the ground path through the Ignition Switch during "BULB TEST" from latching the Low Coolant Relay.

"LOW OIL" INDICATOR
The Instrument Cluster's internal circuitry will only check the Oil Level Sensor at ignition "ON" if Drainback Times are met (35 minutes after ignition "OFF" if the Engine was still cold, or 4 minutes after Ignition "OFF" if the Engine was hot. Hot is defined as running for at least 17 minutes). Drainback Timer sets at Ignition "OFF." The sensor has normally closed contacts that are open under a low oil condition. After determining 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."

"LOW TRAC" INDICATOR
See "Brakes and Traction Control"

OIL PRESSURE GAGE
The Oil Pressure Gage contains internal coils that create magnetic fields when current flows through them. The current through the coils varies depending on the [1][2]Oil Pressure Sensor resistance. (Low pressure resistance is approximately 10 ohms, high pressure resistance is approximately 90 ohms.) The varying sensor resistance causes the current through the coils to fluctuate. The magnetic fields of the coils move the pointer.

"SECURITY" INDICATOR
See "Antitheft & Alarm Systems". Antitheft and Alarm Systems

(MIL) "SERVICE ENGINE SOON" INDICATOR, FOR Z49:
See Computers & Control Systems.

SPEEDOMETER
See "Vehicle Speed Sensor," in Computers and Control Systems. Vehicle Speed Sensor

TACHOMETER
The Tachometer displays engine speed in Revolutions Per Minute (RPM). Voltage pulses from the Ignition system 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.

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.