Circuit Operation

See the circuit referred to for the complete operation of an Indicator and the other components that work with it. Only the Indicators that do not appear in other schematics are described in this section.

Oil Pressure Indicator

The Oil Pressure Indicator comes on to warn the driver when the engine oil pressure is low. Battery voltage is applied to one side of the bulb. A ground path is provided by the Oil Pressure Switch. It closes when the oil pressure is below 27 kPa (4 PSI) and the indicator bulb lights.

After the engine starts and normal oil pressure builds up, the Oil Pressure Switch opens. The Oil Pressure Indicator goes out.

Coolant Temperature Indicator

The Coolant Temperature indicator warns the driver of a high coolant temperature. With the ignition Switch in RUN, BULB TEST or START. voltage from Fuse 11 is applied to the Coolant Temperature indicator. The bulb is grounded through the Coolant Temperature Switch. The switch closes when the coolant temperature exceeds 258°F (126°C) and the bulb lights.

Upshift Indicator

With the 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 manifold vacuum to compute an efficient shift point.

Service Engine Soon Indicator

The SERVICE ENG SOON Indicator serves as a warning light to tell the driver that a problem has occurred and that the car should be serviced. It is also used by the technician to read out diagnostic codes to help diagnose system problems.

The Indicator receives battery voltage in RUN, BULB TEST and START. The ECM provides a switched path to ground.

Low Coolant Indicator

The LOW COOLANT Indicator comes on to warn the driver when a low level of coolant exists in the radiator. Battery voltage is applied in BULB TEST and START. The ECM provides a switched path to ground.

Speedometer and Odometer Displays

The Vehicle Speed Sensor (VSS) generates a signal that indicates the speed of the vehicle. The signal is processed by the Solid State ECM to supply inputs to the Trip Computer, Cruise Control Module, Speedometer and Odometer.

The Vehicle Speed Sensor is mounted in the transaxle. A magnet rotates near a coil, producing voltage pulses in the coil. The frequency of the AC voltage coming from this coil depends on the vehicle speed. The VSS sends pulses to the ECM at the rate of 40,000 pulses per mile.

The ECM takes the voltage pulses from the Vehicle 5peed Sensor and uses them to close a Solid State output switch. The output terminal is switched to ground at a rate that is proportional to the speed of the car. The Speedometer and Odometers are switched at 4000 pulses per mile.

The Speedometer and the Odometer are operated by a circuit board in the cluster. This circuit board converts the pulses received from the ECM into a control signal for the Liquid Crystal Display (LCD) Displays.

Voltmeter

The Voltmeter measures the electrical system voltage with the Ignition Switch in RUN, BULB TEST or START. With the engine stopped , the Voltmeter indicates Battery condition. With the engine running, the Voltmeter indicates Charging System operation.

Tachometer

The Tachometer displays engine speed in rpm. Voltage pulses are taken from the Ignition System and sent to the Tachometer. It responds to the frequency of the voltage pulses which increase with engine speed. Solid State circuits process these pulses into a signal that drives the pointer of the meter.

Fuel Gage

The variable resistor in the fuel tank is changed by the amount of fuel in the tank. With a full tank, the resistance is 90 ohms. It is 0 ohms with the tank empty

This changing resistance changes the current flow through the coils in the Fuel Gage. The coils move the pointer in the Gage.

Oil Pressure Gage

The engine oil pressure is displayed by the Oil Pressure Gage. The pointer of the gage is moved by two coils, and its operation is similar to that of the fuel Gage.

The Fuel Pump/Oil Pressure Sender/Switch is connected to the junction of the two coils. It has low resistance when the oil pressure is low, and 90 ohms resistance when the oil pressure is high. This changing resistance changes the current flow through the coils to move the pointer from 0 to 80 psi.

Coolant Temperature Gage

The Coolant Temperature Gage is also operated by two coils. Battery voltage is applied to both coils. One is grounded directly and the other is grounded through the Coolant Temperature Sender.This has 60 ohms resistance at 280°F (hot coolant) and its resistance increases at lower temperatures. Resistance is approximately 1400 ohms at 100°F. This causes the current through the Sender and one coil to increase as the coolant temperature increases. This moves the pointer.