Principles of Operation

Principles of Operation
The instrument cluster carries out a display prove out to verify that all warning/indicator lamps and monitored systems are operating correctly. When the ignition switch is turned to the ON position with the engine off, the following indicators will illuminate:
- SERVICE ENGINE SOON warning indicator
- charge system warning indicator
- THEFT indicator (Excursion only)
- anti-lock brake system (ABS) warning indicator
- safety belt warning indicator (60 second prove Out)
- air bag indicator
- WAIT TO START indicator (diesel only)

Gauge Indication Systems
The gauge indication systems use magnetic gauges mounted in the instrument cluster. No adjustment, calibration, or maintenance is required for any gauges. The gauges cannot be installed separately.

Instrument Cluster Replacement
When instrument cluster replacement is necessary, contact the Instrument Cluster Program at 1-800-259-9700 (U.S.) or 1-800-663-9974 (Canada).

Fuel Gauge Indication (bi-fuel only)

NOTE: If the bi-fuel vehicle does not operate correctly in alternative fuel mode, refer to Computers and Control Systems.

A single fuel gauge is used for both alternative fuel and gasoline level indication. The fuel indication system uses a fuel pump intercept harness, compuvalve, dash reset relay, Liquid Petroleum Gas (LPG) sensor, Compressed Natural Gas (CNG) Fuel Tank Pressure Sensor (FTPS) combined with the gasoline fuel pump and fuel sensing circuitry. On all the bi-fuel vehicles, the gasoline fuel pump module information is intercepted and routed through the compuvalve. In the gasoline operating mode, the fuel sender information is passed thorough the compuvalve to the instrument cluster fuel gauge. In alternative fuel mode the compuvalve receives the alternate fuel level signal and sends it to the instrument cluster fuel level gauge.

Fuel Sending Unit
The fuel sending unit is a variable resistor controlled by the action of a float arm. When the fuel level is low, resistance in the unit is low. When the fuel level is high, the resistance is high.

Water Temperature Indicator Sender Unit
When the engine temperature is low, the resistance of the water temperature indicator sender unit is high, thus 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.

Oil Pressure Indicator Sender Unit
The oil pressure indicator sender unit consists of a diaphragm and contact points. The contact points are closed with oil pressure causing the gauge to indicate NORMAL oil pressure. With no oil pressure, the contacts open and the gauge indicates low oil pressure.

Charge Indicator System
The battery voltage gauge measures the voltage potential at the battery.

Charge System Warning Indicator
A red charge indicator is located in the instrument cluster. This indicator illuminates when there is low or no generator output.

When the ignition switch contacts are closed, battery current flows through the charge indicator and the parallel resistor (390 ohms) to the voltage indicator, and the indicator comes on.

When the generator builds up enough voltage to energize a circuit in the voltage regulator, the indicator turns off.

Vehicle Speed Sensor (VSS)
On vehicles equipped with 4-Wheel Anti-lock Brake Systems (4WABS), the vehicle speed signal is generated by the rear anti-lock brake sensor and sent to the 4WABS module. The 4WABS module sends the vehicle speed signal via circuit 679 (GY/BK) to all systems that require a vehicle speed signal input. Vehicles equipped with Rear Anti-Lock Brakes (RABS) generate a vehicle speed signal from the rear axle speed sensor. The Generic Electronic Module (GEM) receives this signal (VSS_GEM) for internal use and then distributes it to the appropriate other users (i.e., the powertrain control module speed control module, and speedometer).

Speedometer
The electronic speedometer receives a speed signal from the 4WABS module (if equipped with 4WABS) or the generic electronic module (GEM)/Central Timer Module (CTM) (if equipped with RABS).

Odometer
A million-mile tamper-resistant odometer is standard. New speedometers have a resettable odometer.

NOTE: When installing a new instrument cluster some state laws require that the new odometer must register the same as the removed odometer.

If the actual vehicle mileage cannot be determined, the repair centers are able to supply odometers set to "0" miles. An odometer mileage sticker is supplied with the new instrument cluster. This sticker must display the estimated vehicle mileage and be affixed to the driver doorjamb.

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

Tachometer
Gasoline vehicles are equipped with a 6,000 rpm tachometer and diesel vehicles are equipped with a 4,500 rpm tachometer. Diesel vehicles receive the tachometer signal from the generator. All others receive the tachometer signal from the PCM.

Warning Indicators

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

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

Service Engine Soon Warning Indicator
The SERVICE ENGINE SOON warning indicator is illuminated when a Diagnostic Trouble Code (DTC) is sensed in the closed loop by the Powertrain Control Module (PCM).

Air Bag
If an air bag system DTC is detected, the air bag indicator is illuminated (except Motorhome).

Safety Belt
The safety belt warning indicator is powered through the generic electronic module (GEM). When the ignition key is turned on, the indicator illuminates for four to eight seconds even if the safety belt is buckled.

Low Fuel
When the fuel level drops to a predetermined level, the low fuel warning indicator will illuminate.

Door Ajar
The DOOR AJAR indicator illuminates when any of the vehicle doors are open.

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

Speed Control
The speed control indicator (CRUISE) will illuminate when the speed control is engaged.

Water in Fuel (Diesel only)
The WATER IN FUEL indicator will illuminate when 100 cc (0.2 pints) of water has accumulated in the fuel filter/water separator. The WATER IN FUEL indicator will prove out when the ignition switch is in the START position.

Wait to Start (Diesel only)
The WAIT TO START indicator will illuminate when the ignition switch is in the ON position with the engine OFF while the glow plugs are heating.

Theft (Excursion only)
The theft indicator will flash when the PATS system is activated and will prove out for three seconds when the ignition switch is turned to the ON position.

Warning Indicators-Engine Oil Pressure, Engine Coolant Temperature, Low Fuel
The engine oil pressure warning indicator will illuminate if the engine oil pressure drops below approximately 42 kPa (6 psi).

The engine coolant temperature warning indicator will illuminate if the engine temperature exceeds approximately 121° C (250° F).

The low fuel warning indicator will illuminate if the fuel level drops below approximately 4-8L (1-2 gal).