Principles of Operation

PRINCIPLES OF OPERATION

When installing a new instrument cluster, it is necessary to upload the module configuration to the diagnostic tool. Following installation of the instrument cluster, download the module configuration from the diagnostic tool into the new instrument cluster.The following items are configurable:
- fuel tank size
- number of engine cylinders
- vehicle type (4x2 or 4x4)
- beltminder status

Late build instrument clusters are calibration updatable. To determine if a vehicle is equipped with a late build instrument cluster, refer to the diagnostic tool.

The instrument cluster carries out a display prove-out to verify that all warning/indicator lamps and monitored systems are functioning correctly. When the ignition switch is cycled to the ON position with the engine off, the following indicators illuminate:
- air bag warning indicator (6 second prove-out)
- safety belt warning indicator (illuminated for 65 seconds if safety belt is unbuckled, turns off when safety belt is buckled)
- speed control indicator
- 4x4 HIGH indicator
- 4x4 LOW indicator
- charge system warning indicator
- check fuel cap warning indicator
- low fuel level warning indicator (3 second prove-out)
- low oil pressure warning indicator (illuminated until engine is started)
- check engine/malfunction indicator lamp (MIL)
- ABS warning indicator (3 second prove-out)
- BRAKE warning indicator (3 second prove-out)
- door ajar warning indicator
- O/D OFF indicator

Fuel Gauge
The fuel gauge is an ohmmeter that reads the resistance of the fuel sending unit. The fuel sending unit is a variable resistor which is controlled by the action of a float arm. When the fuel level is low, resistance in the unit is low (22.4 ohms). When the fuel level is high, the resistance is high (145 ohms). Proper fuel gauge indication requires the ignition switch to be in the OFF or ACC positions during refueling, otherwise correct fuel indication after refueling can be slow to update. A minimum of 3 gallons of fuel is needed for correct fuel gauge indication after refueling.

Water Temperature Indicator Gauge
The water temperature indicator gauge is an ohmmeter that reads the resistance of the water temperature indicator sending unit. When the engine temperature is low, the resistance of the water temperature indicator sender is high, restricting the flow of current through the gauge and moving the pointer only a short distance. As the temperature of the coolant increases, the resistance decreases, allowing more current to flow through the gauge and resulting in a corresponding movement of the pointer.

Speedometer
The output shaft speed sensor (OSS) generates and transmits the vehicle speed signal (VSS) data to the powertrain control module (PCM). The PCM sends the VSS data to the instrument cluster and all other systems that require VSS input. The instrument cluster, upon receipt of the VSS signal, commands the speedometer pointer to the corresponding position.

Odometer

NOTE: If the instrument cluster is serviced or replaced new, the previous mileage has to be downloaded to display the correct odometer mileage.

The odometer function is to sum the distance traveled and display the total vehicle distance traveled over a range from 000000 to 999999 either in miles or kilometers.

Trip Odometer
The trip odometer indicates how many miles the vehicle has been driven since the last reset.

Tachometer
The tachometer indicates engine speed in revolutions per minute (rpm) in a range from 0 to 7,000 rpm. The tachometer receives a signal sent from the PCM.

Warning Indicators

Brake Warning Indicator
All vehicles use a brake system warning indicator in the instrument panel to warn of system concerns. The red brake warning light (BRAKE) is used to indicate a low fluid level, a brake concern, or a parking brake that is not fully released. The brake fluid level switch is located in the brake fluid reservoir.

The yellow anti-lock brake system (ABS) warning indicator is used to indicate a concern or deactivation of the ABS. It illuminates when triggered by the ABS control module, and stays illuminated as long as the concern remains in the system.

Low Oil Pressure Warning Indicator
The oil pressure switch installed in the engine block is a resistive switch. A resistance of greater than 1,000 ohms causes the low oil pressure warning indicator to indicate normal oil pressure. A resistance of less than 1000 ohms causes the low oil pressure warning indicator to indicate low oil pressure.

Charge System Warning Indicator
A red charge indicator is located in the instrument cluster. When the generator output is insufficient to maintain the battery state of charge, the instrument cluster illuminates the charging system indicator.

Check Engine/Malfunction Indicator Lamp (MIL)
The MIL is illuminated when a diagnostic trouble code (DTC) is detected by the PCM.

Air Bag Warning Indicator
The instrument cluster is hardwired to the restraint control module (RCM). If an air bag system concern is detected, a DTC is logged and the RCM provides a ground path to the instrument cluster, illuminating the air bag indicator.

Safety Belt Warning Indicator
The safety belt warning indicator is controlled through the instrument cluster. When the ignition switch is turned to the RUN or START position during the first 65 seconds, the indicator illuminates if the safety belt remains unbuckled.

Low Fuel
If a problem with the fuel level input circuit occurs or fuel level drops to a predetermined level, the low fuel indicator illuminates.

Door Ajar
The door ajar indicator illuminates when any of the vehicle doors are open.

High Beam
The high beam indicator is illuminated when the high beams are on.

Overdrive Off
The O/D OFF indicator is a dual function indicator. It illuminates when the transmission overdrive is turned off and blinks off and on if a transmission fault is detected.

Speed Control
The speed control indicator lamp illuminates when the speed control is engaged.

Check Fuel Cap
The check fuel cap indicator is used to indicate leaks in the fuel tank evaporative system that exceed specifications. Fuel tank pressure is monitored by the PCM and if a leak is detected it signals a fault by illuminating the check fuel cap indicator. If a fault is detected, the PCM provides the check fuel cap indicator with a ground.

4x4 HIGH/LOW
With the 4WD mode switch in the 4WD position, the 4x4 indicator illuminates. With the 4WD mode switch in the 4WD low position, the 4x4 LOW indicator illuminates. The 4WD control module communicates status over circuits 783 (GY) 4WD HIGH and 784 (LB/BK) 4WD LOW.