Circuit Operation
"CHECK GAGE" INDICATORWhen the Ignition Switch is in "RUN" and Engine oil pressure is at 0-3 psi, if the Generator voltage is below 10 V or above 16 V or Engine coolant temperature exceeds 140°C (255°F), the Instrument Cluster Logic Chip turns the "CHECK GAGE" Indicator "ON."
FUEL GAGE
The Fuel Gage pointer is controlled by varying the Fuel Level Sender resistance. With the Ignition Switch in "RUN," voltage is applied from I/P Fuse #11 to the Empty coil of the Fuel Gage and divides into two paths: 1) through the Fuel Sender to ground, and 2) through the Full coil to ground. The Gage pointer is controlled by changes of the Fuel Sender resistance. When the Fuel Gage resistance decreases, more current flows through the Fuel Sender and the Empty coil. At the same time, the current through the Full coil decreases.
With two coils operating the pointer, the gage is not affected by changes in the voltage of the system.
COOLANT TEMPERATURE GAGE
The Coolant Temperature Gage applies voltage from CKT 135 to the Engine Coolant Temperature Gage Sensor. The Engine Coolant Temperature Gage Sensor contains a variable resistor. At 405°C (1005°F) the resistance is approximately 1365 ohms and at 1255°C (2605°F) the resistance is approximately 55 ohms. As the resistance of the Engine Coolant Temperature Gage Sensor decreases, the Coolant Temperature Gage senses a smaller voltage drop across the Engine Coolant Temperature Gage Sensor, indicating a higher coolant temperature. As the resistance of the Engine Coolant Temperature Gage Sensor increases, the Coolant Temperature Gage senses a larger voltage drop across the Engine Coolant Temperature Gage Sensor, indicating a lower coolant temperature.
OIL PRESSURE GAGE (NON-SEO)
A two position switch opens with oil pressure greater than approximately 24 kPa (3 psi), directing current flow in CKT 31 through a 68 ohm resistor to ground. This causes the Oil Pressure Gage to deflect approximately 3/4 scale.
VOLTMETER
The voltmeter senses Ignition voltage on CKT 241 and is grounded on CKT 351.
DIGITAL SPEEDOMETER
The Digital Speedometer Display uses a vacuum fluorescent display to show vehicle speed only. With the Ignition Switch in "RUN," current flows from I/P Fuse #20 to the Instrument Cluster connector C2. For 3 seconds, the entire display lights up to check all segments. After the segment check, only the vehicle speed data is displayed.
"GATE AJAR" INDICATOR
B+ is applied at all times to Instrument Cluster connector C2 terminal "B6," powering the "GATE AJAR" Indicator. CKT 146 connects this indicator to the Endgate Lower Lock Ajar Switch. When this switch closes to ground, the "GATE AJAR" Indicator comes "ON."
Instrument Cluster: Digital Chart:
"LOW OIL LEVEL" INDICATOR
The "LOW OIL LEVEL" Indicator ground is controlled by the Powertrain Control Module (PCM). The PCM also supplies B+ to the Engine Oil Level Sensor, mounted in the Engine oil pan. The PCM will not check for a low oil condition until the drop in Engine Coolant Temperature corresponds with the chart shown. The PCM compares the drop in coolant temperature from the last Ignition "OFF" cycle to the coolant temperature at the start of the current Ignition "ON" cycle.
If the coolant temperature drop conditions are not met, the "LOW OIL LEVEL" Indicator will come on for the 2 second bulb test only. (The Ignition must be "'OFF" for a minimum of 5 seconds before the "LOW OIL LEVEL" Indicator can come "ON" again.) If the Indicator is "ON" because of a low oil condition, it will remain "ON" for the rest of the current Ignition Cycle, even if oil is added to the crankcase. A low oil condition exists with 2 3/4 or less quarts of oil remaining in Engine Oil Pan.
OIL PRESSURE GAGE (SEO)
SEO vehicles use a Fuel Pump Switch and Engine Oil Pressure Gage Sensor to allow for a constant reading of the engines oil pressure. The resistance of the sensing portion varies from 1 to 88 ohms.
"LOW COOLANT" INDICATOR
Ignition voltage is applied at all times to the Low Engine Coolant Indicator Probe. A magnetic float in the Coolant Recovery Reservoir rises and falls with the coolant level. A serviceable Reed-Type Switch (mounted in the bottom of the reservoir) senses the floating magnet. When the float (magnet) position gets lower in the reservoir, the Switch contacts are pulled together, grounding CKT 68.
"LOW FUEL" INDICATOR
The Instrument Cluster Logic Chip monitors the Fuel Sender resistance using CKT 30. When the Fuel Gage registers less than 1/8 tank of fuel, the resistance at terminal "A2" of connector C2 will be approximately 10 ± 2 ohms. If this condition is met for 128 ± 64 seconds, the Logic Chip within the Instrument Cluster will ground the "LOW FUEL" Indicator, causing it to turn "ON." After refuelling, the resistance at terminal "A2" of connector C2 will be above 15 ± 2 ohms, depending on the amount of fuel in the fuel tank. Within the same Ignition Cycle, after approximately 128 ± 64 seconds, the Logic Chip within the Instrument Cluster will turn the "LOW FUEL" Indicator "OFF."
"LOW WASHER FLUID" INDICATOR
When the Ignition Switch is turned to "RUN," voltage is applied to the Windshield Washer Solvent Level Switch. If washer solvent level is low, the Windshield Washer Solvent Level Switch is closes, grounding CKT 99. The Instrument Cluster Logic Chip monitors CKT 99. When CKT 99 goes low, the Logic Chip grounds the "LOW WASHER FLUID" Indicator, causing it to turn "ON." Once the indicator has been turned "ON," it will stay "ON" until the windshield washer solvent container has been refilled, causing the Windshield Washer Solvent Level Switch to open. The Ignition Switch must then be cycled from "OFF" to "RUN" for the Indicator to turn "OFF."