Prizm L4-108 1.8L DOHC VIN 8 MFI (1998)
Coolant Temperature Sensor/Switch (For Computer): Description and Operation
Engine Coolant Temperature (ECT) Sensor
Engine Coolant Temperature (ECT) Sensor
The engine coolant temperature (ECT) sensor is a thermistor (a resistor whose resistance changes as a function of temperature) and is mounted in the
engine coolant stream. The ECT has two internal sensors, one portion (a single wire) controls cooling fan operation and is NOT controlled or monitored
by the PCM. The other portion (two wires) is PCM monitored.
The PCM monitored portion of the ECT sensor is a two-wire sensor with a reference voltage and a ground provided by the powertrain control module
(PCM). Low coolant temperature produces a high resistance and high temperatures result in a low resistance.
The PCM supplies a 5 volt signal to the coolant sensor through a resistor in the PCM and measures the signal voltage. The voltage will be high when the
engine is cold and low when the engine is hot.
The ECT sensor provides engine coolant temperature information to the PCM for fuel enrichment, ignition timing, air management, idle speed control
and closed loop fuel control.
