Base Cluster
CIRCUIT OPERATIONOnly those indicators and gauges that are not described in connection with other circuits are explained in this circuit operation. See the circuit referred to for its complete operation.
FUEL GAUGE
The pointer of the Fuel Gauge is moved by the magnetic field of two coils. The coils are at right angles to each other. Battery voltage is applied to the E coil and the circuit divides at the opposite end of this coil. One path continues to ground through the F coil. The other path grounds through the variable resistor of the Fuel Gauge Sender.
When the tank is low, the resistance of the sender is low (0 ohms). A large current passes through the E coil and the Fuel Gauge Sender resistor. This moves the pointer toward E on the scale. When the tank is full, the sender resistance is high (90 ohms). More current flows through the F coil, moving the pointer toward "F" on the scale.
With two coils operating the pointer, the gauge is not affected by changes in the voltage of the system.
ENGINE COOLANT TEMPERATURE GAUGE
The Engine Coolant Temperature Gauge is operated by two coils. Battery voltage is applied to both coils. One is grounded directly and the other is grounded through the Engine Coolant Temperature (ECT) Sender/Switch. This has 55 ohms resistance at 127°C (260°F) (hot coolant) and its resistance increases at lower temperature. Resistance is approximately 1365 ohms at 38°C (1OO°F). This causes the current through the sender and one coil to increase as the coolant temperature increases. This moves the pointer.
SHIFT INDICATOR
In vehicles equipped with Manual Transaxle, a bulb lights when the car should be shifted to the next higher gear for better fuel economy. Battery voltage is applied to one side of the bulb. The other side of the bulb is switched to ground by the ECM which uses engine data such as rpm, vehicle speed, and intake vacuum to compute an efficient shift point.
SPEEDOMETER
The Speedometer pointer is moved by the magnetic field of two coils. These coils are driven by a solid state unit.
The Vehicle Speed Sensor located in the transaxle generates an AC voltage that is sent to the Engine Control Module (ECM). The ECM processes this voltage into a square wave. The pulses generated are sent to the Speedometer at 4000 pulses per mile.
ODOMETER
The Odometer is driven by an electric motor that is fed from the solid state circuit board. The stepper motor turns in response to the number of pulses received from the ECM.
LOW COOLANT INDICATOR
The LOW COOLANT Indicator comes on to warn the driver when a low level of coolant exists in the Surge Tank. Voltage is supplied to the LOW COOLANT Indicator with the Ignition Switch in "RUN," "BULB TEST" or "START." When a low level of coolant exists, the Low Coolant Switch closes, providing ground for the LOW COOLANT Indicator.
OIL PRESSURE INDICATOR
The Oil Pressure Indicator goes "ON" to warn of low oil pressure when the Fuel Pump Switch/Oil Pressure Switch is closed. The Fuel Pump Switch/Oil Pressure Switch is closed when oil pressure falls below 27 kPa (4 psi). When the engine is started, oil pressure is below 27 kPa so the Fuel Pump Switch/Oil Pressure Switch is closed, and the Oil Pressure Indicator goes "ON" momentarily as a bulb test. The Oil Pressure Indicator goes "OFF" as soon as oil pressure is above 27 kPa (4 psi) and the Fuel Pump Switch/Oil Pressure Switch opens.
ENGINE COOLANT TEMPERATURE INDICATOR
The Engine Coolant Temperature Indicator bulb is tested in "BULB TEST" and "START" by grounding through the Ignition Switch. The indicator goes "ON" in "RUN" when the engine coolant temperature is above 258°F (126°C) and the Engine Coolant Temperature (ECT) Sender/Switch.
LOW OIL LEVEL INDICATOR
The LOW OIL LEVEL Indicator lights to warn the driver of low oil level. When the Ignition Switch is first moved to "RUN," the Low Oil Warning Module turns on the LOW OIL LEVEL Indicator for 2 seconds as a bulb check. The LOW OIL LEVEL Indicator remains lit if the oil level is approximately 1 1/2 quarts or more low. The oil level monitoring system consists of the following components:
^ Low Oil Warning Module.
^ LOW OIL LEVEL Indicator.
^ Oil Level Switch.
The Low Oil Warning Module has two internal timers. One timer records the amount of time the ignition has been "OFF" while the other records the amount of time the ignition had been on before the ignition was shut "OFF." The module uses this time information to determine if the engine has been "OFF" long enough for the oil in the engine to have returned to the oil pan.
The module will check the Oil Level Switch to determine oil level if one of the two following conditions are met:
1. The ignition has been "OFF" for more than 32 minutes.
2. The ignition has been "OFF" for at least 3 minutes after the ignition has been "ON" for at least 12 minutes.
If the oil level is low (Oil Level Switch open), the Low Warning Module grounds the Low Oil Indicator, causing it to remain lit for the remainder of the ignition cycle. The Low Oil Warning Module only checks the oil level when the Ignition Switch is first moved to "RUN." It does not continuously monitor the oil level.
The Oil Level Switch is an assembly containing a reed switch and magnetic float. When the oil level is normal, the float rests near the reed switch, causing the switch to close. When the oil level is low, the float rests away from the reed switch and the switch opens.
NOTE: If battery voltage is removed from and then reconnected to the Low Oil Warning Module term "F" (BAT input), the internal timers will reset. The module will behave as though the ignition has been "OFF" for 32 minutes. In this case, if the engine has been run for a time period other than one of the two listed above, the system may not check the level correctly.