Indicators & Gauges

Circuit Description

The operation of individual indicators is stated below. For indicators not listed below (for instance, door ajar, seat belt, etc.), see the system indicated by the circuit schematic diagrams.

Oil Pressure Indicator
Battery voltage is applied to the indicator bulb from fuse 17 with the ignition in ON or START. When the oil pressure is low, the oil pressure switch closes, providing a ground for the indicator bulb. Due to the oil pressure not present when the engine is not running, and the ignition is ON, the pressure switch remains closed.

CHECK ENGINE Indicator
Battery voltage is applied to the indicator bulb from fuse 17 with the ignition in ON or START. The ground of the indicator is controlled by the engine control module. The control module will light the indicator when the engine is not running or when it detects a problem.

Speedometer
With the ignition switch in ON and START, the speedometer drive circuit receives pulses from the vehicle speed sensor. The pulse rate increases as the car accelerates. The frequency and duration of these input pulses are measured and displayed by the speedometer.

Tachometer
The tachometer displays engine speed in rpm. Voltage pulses are taken from the ignition system and sent to the tachometer by the ECM. The tachometer responds to the frequency of the voltage pulses, which vary according to engine speed.

Indicator Brake
When the ignition switch in ON or START, battery voltage is applied from fuse 17 to the brake warning light. When the brake is applied, the switch closes and provides a ground for the light. The brake warning light goes on to remind the driver that the parking brake is applied. If the brake fluid level is low, the brake fluid level switch closes and ground is provided to the circuit. The brake warning light lights to warn the driver of low brake fluid level in the brake master cylinder. (Note: Check brake pad wear before adding fluid.)

Fuel Gauge
The pointer of the fuel gauge is moved by the magnetic fields of two coils. The coils are at right angles to each other. Battery voltage is applied to the coils through fuse 17, generating the magnetic fields. The magnetic fields, controlled by the fuel gauge sender, causes the gauge needle to move. As the resistance in the sender varies, current through the gauge coils changes. The fuel gauge sender's resistance varies from about 95 at empty to 7 when full

Engine Coolant Temperature Gauge
The pointer of the engine coolant temperature gauge is moved by the magnetic fields of two coils. The coils are at right angles to each other. Battery voltage is applied to the coils through fuse 17, generating the magnetic fields. The magnetic fields, controlled by the engine coolant temperature sender, cause the gauge needle to move. As the resistance in the sender varies, current through the gauge coils changes. The engine coolant temperature sender's resistance varies from about 157 Ohms at 55°C to 24 Ohms at 11O°C.