Engine - Coolant Temperature Sensor/Switch: Description and Operation

Engine Coolant Temperature Sensor:

PURPOSE
Responds to temperature changes of engine coolant and sends a coresponding signal to the powertrain control module engine (PCME).

OPERATION
Sensor is is a thermistor with a negative temperature coefficient; as temperature increases, resistance decreases. PCME detects changes in engine temperature by monitoring the effects the resistance changes make to the applied reference voltage of the engine coolant temperature sensor.
The engine coolant temperature sensor affects the operation of the following PCME output systems and/or devices:
- A/C relay (A/C cut-off control system) and Condenser fan (LOW speed) relay
- Coolant fan relay (coolant fan control)
- Condenser fan (HIGH speed) relays No.1 and No.2
- Fuel injection quantity
- Fuel injection timing
- BAC valve (Idle air control valve-idle speed)
- Purge solenoid valve (purge control)
- EGR control solenoid valves (EGR operation)
- Igniter (ignition timing control)
- Pressure regulator control solenoid valves (fuel pressure)
- Powertrain control module transaxle (torque reduced signal/water thermo-signal)
- Self-diagnosis checker (diagnostic trouble codes)

REMARKS
Diagnostic trouble code 09 will be stored in powertrain control module engine (PCME) memory, if a failure occurs in the engine coolant temperature sensor or its circuit.