Circuit Operation - Instrument Cluster

"OIL" PRESSURE INDICATOR
The "OIL PRESSURE" Indicator bulb will ground at the Fuel Pump Switch and Engine Oil Pressure Gage Sensor, when Engine oil pressure drops below 4 lbs.

"HOT" COOLANT TEMPERATURE INDICATOR
The "HOT" Coolant Temperature Indicator comes "ON" to warn the driver of high coolant temperature.

With the Ignition Switch in "RUN," "BULB TEST" or "START," voltage from I/P Fuse #11 is applied to the "HOT" Coolant Temperature Indicator. In "BULB TEST" or "START," the lamp is grounded through the Instrument Cluster Logic Chip so that the bulb can be tested. In "RUN," the current path is also completed through the Logic Chip in the Instrument Cluster. The Engine Coolant Temperature Gage Sensor resistance will be low when the coolant temperature exceeds 1265°C (2585°F) causing the Logic Chip to command the lamp "ON."

FUEL GAGE
With the Ignition Switch in "RUN," "BULB TEST" or "START," voltage is applied from I/P Fuse #11 to the Fuel Gage. The Fuel Gage pointer is controlled by varying the Fuel Sender resistance. Voltage is applied from Fuse #11 to the Empty coil of the Fuel Gage and divides into two paths: 1) through the Fuel Gage Sender to ground, and 2) through the Full coil to ground. The Gage pointer is controlled by changes in the Sender's resistance. When the Fuel Gage resistance decreases, more current flows through the 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 385°C (1005°F) the resistance is approximately 1365 ohms and at 1275°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 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.

"GATE AJAR" INDICATOR
Voltage is applied at all times to the "GATE AJAR" indicator from I/P Fuse #33. When the Endgate is opened, (as a door) the "GATE AJAR" Switch closes completing the path to ground and turns the indicator "ON."

Chart: Instrument Cluster:

"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 above. 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 seconds 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.

"LOW COOLANT LEVEL" 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 WASH FLUID" LEVEL 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, and the Windshield Washer Solvent Level Switch is closed, ground is applied to the "LOW WASH FLUID" Indicator. 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."

"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 refueling, 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

SPEEDOMETER
The Speed Sensor Circuit consists of a magnetic type sensor and wiring. Gear teeth pressed on the Transmission Output Shaft induce an alternating current in the sensor. This sensor generates a sine wave output with a frequency proportional to vehicle speed. The PCM converts this signal to an output that is switched to ground at a frequency of 4000 pulses per mile at the DK GRN/WHT wire (CKT 817), which feeds the Turn Signal Alarm, Power Steering Control Module, Instrument Cluster, Cruise Control Module and Radio (Chev only).