Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Coolant Temperature Sensor/Switch (For Computer): Description and Operation
1993 Geo Prizm L4-1600cc 1.6L DOHCSECTION Description and Operation
Coolant Temperature Sensor (CTS):
The Engine Coolant Temperature Sensor (ECT) is a thermistor (a resistor whose resistance changes as a function of temperature) and is mounted in the coolant stream. The ECT is a two wire sensor with a referance voltage and a ground provided by the ECM. Low coolant temperature produces a high resistance and high temperatures result in a low resistance.
The ECM supplies a five-volt signal to the sensor through a resistor in the ECM 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 coolant temperature information to the ECM for fuel enrichment, ignition timing, air management , idle speed control and closed loop fuel control.
A failure in the ECT sensor circuit should set a Diagnostic Trouble Code (DTC) 22.
RENDER: 1.0x
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.